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 $7.30   5.535%   $7.7041   $7.70   $7.70   $7.70  
  Purchase #2 $133.55   6.456%   $142.172   $142.17   $142.15   $142.20  
  Purchase #3 $14.36   9.263%   $15.6902   $15.69   $15.70   $15.70  
  Purchase #4 $103.61   8.404%   $112.3174   $112.32   $112.30   $112.30  
  Purchase #5 $212.71   12.252%   $238.7712   $238.77   $238.75   $238.80  
  Purchase #6 $105.44   10.802%   $116.8296   $116.83   $116.85   $116.80  
  Purchase #7 $236.59   10.386%   $261.1622   $261.16   $261.15   $261.20  
  7 purchase totals = $813.56       $894.6467   $894.64   $894.60   $894.70