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 $6.40   12.834%   $7.2214   $7.22   $7.20   $7.20  
  Purchase #2 $31.56   4.645%   $33.026   $33.03   $33.05   $33.00  
  Purchase #3 $47.54   5.855%   $50.3235   $50.32   $50.30   $50.30  
  Purchase #4 $183.75   11.419%   $204.7324   $204.73   $204.75   $204.70  
  Purchase #5 $154.49   10.313%   $170.4226   $170.42   $170.40   $170.40  
  Purchase #6 $66.66   10.125%   $73.4093   $73.41   $73.40   $73.40  
  Purchase #7 $178.44   6.333%   $189.7406   $189.74   $189.75   $189.70  
  7 purchase totals = $668.84       $728.8758   $728.87   $728.85   $728.70