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 $48.57   3.361%   $50.2024   $50.20   $50.20   $50.20  
  Purchase #2 $119.38   11.173%   $132.7183   $132.72   $132.70   $132.70  
  Purchase #3 $112.92   4.332%   $117.8117   $117.81   $117.80   $117.80  
  Purchase #4 $225.84   13.421%   $256.15   $256.15   $256.15   $256.20  
  Purchase #5 $84.75   10.701%   $93.8191   $93.82   $93.80   $93.80  
  Purchase #6 $217.51   9.777%   $238.776   $238.78   $238.80   $238.80  
  Purchase #7 $119.25   11.229%   $132.6406   $132.64   $132.65   $132.60  
  7 purchase totals = $928.22       $1,022.1181   $1,022.12   $1,022.10   $1,022.10