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 $70.64   3.867%   $73.3716   $73.37   $73.35   $73.40  
  Purchase #2 $138.48   9.193%   $151.2105   $151.21   $151.20   $151.20  
  Purchase #3 $103.51   12.354%   $116.2976   $116.30   $116.30   $116.30  
  Purchase #4 $48.49   6.383%   $51.5851   $51.59   $51.60   $51.60  
  Purchase #5 $232.96   5.263%   $245.2207   $245.22   $245.20   $245.20  
  Purchase #6 $44.75   13.869%   $50.9564   $50.96   $50.95   $51.00  
  Purchase #7 $167.66   4.574%   $175.3288   $175.33   $175.35   $175.30  
  7 purchase totals = $806.49       $863.9707   $863.98   $863.95   $864.00