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 $53.53   9.557%   $58.6459   $58.65   $58.65   $58.60  
  Purchase #2 $55.58   13.400%   $63.0277   $63.03   $63.05   $63.00  
  Purchase #3 $152.75   11.148%   $169.7786   $169.78   $169.80   $169.80  
  Purchase #4 $215.82   3.341%   $223.0305   $223.03   $223.05   $223.00  
  Purchase #5 $116.25   9.230%   $126.9799   $126.98   $127.00   $127.00  
  Purchase #6 $92.51   5.863%   $97.9339   $97.93   $97.95   $97.90  
  Purchase #7 $104.91   11.813%   $117.303   $117.30   $117.30   $117.30  
  7 purchase totals = $791.35       $856.6995   $856.70   $856.80   $856.60