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 $62.95   6.267%   $66.8951   $66.90   $66.90   $66.90  
  Purchase #2 $210.97   6.523%   $224.7316   $224.73   $224.75   $224.70  
  Purchase #3 $104.84   13.601%   $119.0993   $119.10   $119.10   $119.10  
  Purchase #4 $190.79   5.584%   $201.4437   $201.44   $201.45   $201.40  
  Purchase #5 $24.59   4.784%   $25.7664   $25.77   $25.75   $25.80  
  Purchase #6 $207.90   10.437%   $229.5985   $229.60   $229.60   $229.60  
  Purchase #7 $140.41   13.378%   $159.194   $159.19   $159.20   $159.20  
  7 purchase totals = $942.45       $1,026.7286   $1,026.73   $1,026.75   $1,026.70