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 $225.77   10.568%   $249.6294   $249.63   $249.65   $249.60  
  Purchase #2 $113.49   6.785%   $121.1903   $121.19   $121.20   $121.20  
  Purchase #3 $140.66   13.661%   $159.8756   $159.88   $159.90   $159.90  
  Purchase #4 $102.70   13.574%   $116.6405   $116.64   $116.65   $116.60  
  Purchase #5 $25.98   11.393%   $28.9399   $28.94   $28.95   $28.90  
  Purchase #6 $126.53   10.835%   $140.2395   $140.24   $140.25   $140.20  
  Purchase #7 $190.60   8.566%   $206.9268   $206.93   $206.95   $206.90  
  7 purchase totals = $925.73       $1,023.4420   $1,023.45   $1,023.55   $1,023.30