Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $204.42   10.539%   $225.9638   $225.96   $225.95   $226.00  
  Purchase #2 $175.40   11.706%   $195.9323   $195.93   $195.95   $195.90  
  Purchase #3 $237.65   12.803%   $268.0763   $268.08   $268.10   $268.10  
  Purchase #4 $147.57   4.743%   $154.5692   $154.57   $154.55   $154.60  
  Purchase #5 $149.94   9.831%   $164.6806   $164.68   $164.70   $164.70  
  Purchase #6 $162.83   11.246%   $181.1419   $181.14   $181.15   $181.10  
  Purchase #7 $214.69   10.343%   $236.8954   $236.90   $236.90   $236.90  
  7 purchase totals = $1,292.50       $1,427.2595   $1,427.26   $1,427.30   $1,427.30