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 $51.46   8.742%   $55.9586   $55.96   $55.95   $56.00  
  Purchase #2 $226.91   8.210%   $245.5393   $245.54   $245.55   $245.50  
  Purchase #3 $68.30   12.306%   $76.705   $76.71   $76.70   $76.70  
  Purchase #4 $128.98   7.622%   $138.8109   $138.81   $138.80   $138.80  
  Purchase #5 $5.55   10.219%   $6.1172   $6.12   $6.10   $6.10  
  Purchase #6 $18.30   12.544%   $20.5956   $20.60   $20.60   $20.60  
  Purchase #7 $135.59   5.836%   $143.503   $143.50   $143.50   $143.50  
  7 purchase totals = $635.09       $687.2296   $687.24   $687.20   $687.20