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 $201.49   11.762%   $225.1893   $225.19   $225.20   $225.20  
  Purchase #2 $56.51   5.106%   $59.3954   $59.40   $59.40   $59.40  
  Purchase #3 $116.53   3.106%   $120.1494   $120.15   $120.15   $120.10  
  Purchase #4 $113.87   5.193%   $119.7833   $119.78   $119.80   $119.80  
  Purchase #5 $86.37   9.468%   $94.5475   $94.55   $94.55   $94.50  
  Purchase #6 $66.68   9.731%   $73.1686   $73.17   $73.15   $73.20  
  Purchase #7 $144.85   10.218%   $159.6508   $159.65   $159.65   $159.70  
  7 purchase totals = $786.30       $851.8843   $851.89   $851.90   $851.90