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 $55.95   4.717%   $58.5892   $58.59   $58.60   $58.60  
  Purchase #2 $216.31   10.788%   $239.6455   $239.65   $239.65   $239.60  
  Purchase #3 $32.60   8.337%   $35.3179   $35.32   $35.30   $35.30  
  Purchase #4 $90.97   9.288%   $99.4193   $99.42   $99.40   $99.40  
  Purchase #5 $42.99   3.445%   $44.471   $44.47   $44.45   $44.50  
  Purchase #6 $65.29   7.689%   $70.3101   $70.31   $70.30   $70.30  
  Purchase #7 $190.94   13.234%   $216.209   $216.21   $216.20   $216.20  
  7 purchase totals = $695.05       $763.9620   $763.97   $763.90   $763.90