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 $98.84   4.163%   $102.9547   $102.95   $102.95   $103.00  
  Purchase #2 $93.54   3.669%   $96.972   $96.97   $96.95   $97.00  
  Purchase #3 $84.49   7.590%   $90.9028   $90.90   $90.90   $90.90  
  Purchase #4 $61.72   5.650%   $65.2072   $65.21   $65.20   $65.20  
  Purchase #5 $76.75   3.470%   $79.4132   $79.41   $79.40   $79.40  
  Purchase #6 $249.93   10.397%   $275.9152   $275.92   $275.90   $275.90  
  Purchase #7 $221.35   5.315%   $233.1148   $233.11   $233.10   $233.10  
  7 purchase totals = $886.62       $944.4799   $944.47   $944.40   $944.50