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 $54.46   12.104%   $61.0518   $61.05   $61.05   $61.10  
  Purchase #2 $25.89   10.486%   $28.6048   $28.60   $28.60   $28.60  
  Purchase #3 $203.97   6.522%   $217.2729   $217.27   $217.25   $217.30  
  Purchase #4 $212.94   8.828%   $231.7383   $231.74   $231.75   $231.70  
  Purchase #5 $164.97   12.630%   $185.8057   $185.81   $185.80   $185.80  
  Purchase #6 $118.62   6.673%   $126.5355   $126.54   $126.55   $126.50  
  Purchase #7 $118.90   10.723%   $131.6496   $131.65   $131.65   $131.60  
  7 purchase totals = $899.75       $982.6586   $982.66   $982.65   $982.60