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 $141.43   5.874%   $149.7376   $149.74   $149.75   $149.70  
  Purchase #2 $224.73   11.380%   $250.3043   $250.30   $250.30   $250.30  
  Purchase #3 $123.41   13.742%   $140.369   $140.37   $140.35   $140.40  
  Purchase #4 $60.54   7.155%   $64.8716   $64.87   $64.85   $64.90  
  Purchase #5 $46.30   7.728%   $49.8781   $49.88   $49.90   $49.90  
  Purchase #6 $204.97   4.289%   $213.7612   $213.76   $213.75   $213.80  
  Purchase #7 $61.48   6.464%   $65.4541   $65.45   $65.45   $65.50  
  7 purchase totals = $862.86       $934.3759   $934.37   $934.35   $934.50