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 $58.55   10.117%   $64.4735   $64.47   $64.45   $64.50  
  Purchase #2 $71.62   4.289%   $74.6918   $74.69   $74.70   $74.70  
  Purchase #3 $159.93   6.772%   $170.7605   $170.76   $170.75   $170.80  
  Purchase #4 $15.99   6.472%   $17.0249   $17.02   $17.00   $17.00  
  Purchase #5 $196.97   4.592%   $206.0149   $206.01   $206.00   $206.00  
  Purchase #6 $159.38   11.556%   $177.798   $177.80   $177.80   $177.80  
  Purchase #7 $80.49   5.268%   $84.7302   $84.73   $84.75   $84.70  
  7 purchase totals = $742.93       $795.4938   $795.48   $795.45   $795.50