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 $192.62   10.589%   $213.0165   $213.02   $213.00   $213.00  
  Purchase #2 $55.55   12.128%   $62.2871   $62.29   $62.30   $62.30  
  Purchase #3 $18.44   8.308%   $19.972   $19.97   $19.95   $20.00  
  Purchase #4 $57.46   11.537%   $64.0892   $64.09   $64.10   $64.10  
  Purchase #5 $201.77   7.834%   $217.5767   $217.58   $217.60   $217.60  
  Purchase #6 $103.70   7.855%   $111.8456   $111.85   $111.85   $111.80  
  Purchase #7 $51.72   11.226%   $57.5261   $57.53   $57.55   $57.50  
  7 purchase totals = $681.26       $746.3132   $746.33   $746.35   $746.30