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 $69.83   8.207%   $75.5609   $75.56   $75.55   $75.60  
  Purchase #2 $43.41   10.498%   $47.9672   $47.97   $47.95   $48.00  
  Purchase #3 $92.49   9.144%   $100.9473   $100.95   $100.95   $100.90  
  Purchase #4 $210.33   7.184%   $225.4401   $225.44   $225.45   $225.40  
  Purchase #5 $8.84   11.549%   $9.8609   $9.86   $9.85   $9.90  
  Purchase #6 $141.62   12.650%   $159.5349   $159.53   $159.55   $159.50  
  Purchase #7 $31.56   11.510%   $35.1926   $35.19   $35.20   $35.20  
  7 purchase totals = $598.08       $654.5039   $654.50   $654.50   $654.50