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 $146.36   4.173%   $152.4676   $152.47   $152.45   $152.50  
  Purchase #2 $98.69   9.615%   $108.179   $108.18   $108.20   $108.20  
  Purchase #3 $144.50   3.353%   $149.3451   $149.35   $149.35   $149.30  
  Purchase #4 $80.68   12.428%   $90.7069   $90.71   $90.70   $90.70  
  Purchase #5 $82.33   5.283%   $86.6795   $86.68   $86.70   $86.70  
  Purchase #6 $197.45   4.268%   $205.8772   $205.88   $205.90   $205.90  
  Purchase #7 $174.38   4.443%   $182.1277   $182.13   $182.15   $182.10  
  7 purchase totals = $924.39       $975.3830   $975.40   $975.45   $975.40