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 $91.42   3.441%   $94.5658   $94.57   $94.55   $94.60  
  Purchase #2 $139.90   10.307%   $154.3195   $154.32   $154.30   $154.30  
  Purchase #3 $46.77   4.423%   $48.8386   $48.84   $48.85   $48.80  
  Purchase #4 $6.97   5.452%   $7.35   $7.35   $7.35   $7.40  
  Purchase #5 $49.92   12.689%   $56.2543   $56.25   $56.25   $56.30  
  Purchase #6 $165.65   11.313%   $184.39   $184.39   $184.40   $184.40  
  Purchase #7 $189.86   5.730%   $200.739   $200.74   $200.75   $200.70  
  7 purchase totals = $690.49       $746.4572   $746.46   $746.45   $746.50