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 $245.75   8.430%   $266.4667   $266.47   $266.45   $266.50  
  Purchase #2 $161.56   13.275%   $183.0071   $183.01   $183.00   $183.00  
  Purchase #3 $102.73   7.779%   $110.7214   $110.72   $110.70   $110.70  
  Purchase #4 $157.59   6.790%   $168.2904   $168.29   $168.30   $168.30  
  Purchase #5 $91.95   10.484%   $101.59   $101.59   $101.60   $101.60  
  Purchase #6 $127.67   10.287%   $140.8034   $140.80   $140.80   $140.80  
  Purchase #7 $104.98   8.144%   $113.5296   $113.53   $113.55   $113.50  
  7 purchase totals = $992.23       $1,084.4086   $1,084.41   $1,084.40   $1,084.40