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 $87.63   6.677%   $93.4811   $93.48   $93.50   $93.50  
  Purchase #2 $32.54   8.694%   $35.369   $35.37   $35.35   $35.40  
  Purchase #3 $242.48   9.574%   $265.695   $265.70   $265.70   $265.70  
  Purchase #4 $31.98   3.855%   $33.2128   $33.21   $33.20   $33.20  
  Purchase #5 $143.93   9.560%   $157.6897   $157.69   $157.70   $157.70  
  Purchase #6 $200.92   12.456%   $225.9466   $225.95   $225.95   $225.90  
  Purchase #7 $202.53   5.726%   $214.1269   $214.13   $214.15   $214.10  
  7 purchase totals = $942.01       $1,025.5211   $1,025.53   $1,025.55   $1,025.50