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 $66.50   4.701%   $69.6262   $69.63   $69.65   $69.60  
  Purchase #2 $235.84   6.187%   $250.4314   $250.43   $250.45   $250.40  
  Purchase #3 $231.85   5.639%   $244.924   $244.92   $244.90   $244.90  
  Purchase #4 $140.98   12.296%   $158.3149   $158.31   $158.30   $158.30  
  Purchase #5 $30.41   7.626%   $32.7291   $32.73   $32.75   $32.70  
  Purchase #6 $104.44   13.548%   $118.5895   $118.59   $118.60   $118.60  
  Purchase #7 $232.73   7.366%   $249.8729   $249.87   $249.85   $249.90  
  7 purchase totals = $1,042.75       $1,124.4880   $1,124.48   $1,124.50   $1,124.40