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 $87.33   8.221%   $94.5094   $94.51   $94.50   $94.50  
  Purchase #2 $44.30   8.159%   $47.9144   $47.91   $47.90   $47.90  
  Purchase #3 $59.91   8.283%   $64.8723   $64.87   $64.85   $64.90  
  Purchase #4 $207.35   12.260%   $232.7711   $232.77   $232.75   $232.80  
  Purchase #5 $115.98   10.307%   $127.9341   $127.93   $127.95   $127.90  
  Purchase #6 $190.63   9.691%   $209.104   $209.10   $209.10   $209.10  
  Purchase #7 $126.45   10.328%   $139.5098   $139.51   $139.50   $139.50  
  7 purchase totals = $831.95       $916.6151   $916.60   $916.55   $916.60