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 $86.87   13.163%   $98.3047   $98.30   $98.30   $98.30  
  Purchase #2 $7.33   6.347%   $7.7952   $7.80   $7.80   $7.80  
  Purchase #3 $60.43   12.432%   $67.9427   $67.94   $67.95   $67.90  
  Purchase #4 $80.43   12.441%   $90.4363   $90.44   $90.45   $90.40  
  Purchase #5 $236.48   4.479%   $247.0719   $247.07   $247.05   $247.10  
  Purchase #6 $182.55   12.185%   $204.7937   $204.79   $204.80   $204.80  
  Purchase #7 $48.75   5.680%   $51.519   $51.52   $51.50   $51.50  
  7 purchase totals = $702.84       $767.8635   $767.86   $767.85   $767.80