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 $111.66   12.464%   $125.5773   $125.58   $125.60   $125.60  
  Purchase #2 $50.70   10.334%   $55.9393   $55.94   $55.95   $55.90  
  Purchase #3 $189.29   8.368%   $205.1298   $205.13   $205.15   $205.10  
  Purchase #4 $74.58   13.265%   $84.473   $84.47   $84.45   $84.50  
  Purchase #5 $168.79   8.278%   $182.7624   $182.76   $182.75   $182.80  
  Purchase #6 $238.45   8.554%   $258.847   $258.85   $258.85   $258.80  
  Purchase #7 $36.31   9.660%   $39.8175   $39.82   $39.80   $39.80  
  7 purchase totals = $869.78       $952.5463   $952.55   $952.55   $952.50