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 $118.67   5.590%   $125.3037   $125.30   $125.30   $125.30  
  Purchase #2 $9.48   5.610%   $10.0118   $10.01   $10.00   $10.00  
  Purchase #3 $189.26   9.535%   $207.3059   $207.31   $207.30   $207.30  
  Purchase #4 $56.90   13.630%   $64.6555   $64.66   $64.65   $64.70  
  Purchase #5 $148.57   10.756%   $164.5502   $164.55   $164.55   $164.60  
  Purchase #6 $46.58   8.143%   $50.373   $50.37   $50.35   $50.40  
  Purchase #7 $9.57   5.687%   $10.1142   $10.11   $10.10   $10.10  
  7 purchase totals = $579.03       $632.3143   $632.31   $632.25   $632.40