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 $43.28   12.172%   $48.548   $48.55   $48.55   $48.50  
  Purchase #2 $13.33   4.231%   $13.894   $13.89   $13.90   $13.90  
  Purchase #3 $166.76   10.856%   $184.8635   $184.86   $184.85   $184.90  
  Purchase #4 $124.54   6.740%   $132.934   $132.93   $132.95   $132.90  
  Purchase #5 $141.76   12.185%   $159.0335   $159.03   $159.05   $159.00  
  Purchase #6 $120.46   4.787%   $126.2264   $126.23   $126.25   $126.20  
  Purchase #7 $195.25   6.164%   $207.2852   $207.29   $207.30   $207.30  
  7 purchase totals = $805.38       $872.7846   $872.78   $872.85   $872.70