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 $237.44   13.143%   $268.6467   $268.65   $268.65   $268.60  
  Purchase #2 $159.41   13.663%   $181.1902   $181.19   $181.20   $181.20  
  Purchase #3 $167.37   6.145%   $177.6549   $177.65   $177.65   $177.70  
  Purchase #4 $246.93   5.359%   $260.163   $260.16   $260.15   $260.20  
  Purchase #5 $133.25   11.626%   $148.7416   $148.74   $148.75   $148.70  
  Purchase #6 $89.76   3.479%   $92.8828   $92.88   $92.90   $92.90  
  Purchase #7 $83.75   4.381%   $87.4191   $87.42   $87.40   $87.40  
  7 purchase totals = $1,117.91       $1,216.6983   $1,216.69   $1,216.70   $1,216.70