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 $16.36   10.648%   $18.102   $18.10   $18.10   $18.10  
  Purchase #2 $246.60   6.153%   $261.7733   $261.77   $261.75   $261.80  
  Purchase #3 $211.63   7.663%   $227.8472   $227.85   $227.85   $227.80  
  Purchase #4 $204.80   6.518%   $218.1489   $218.15   $218.15   $218.10  
  Purchase #5 $100.41   10.422%   $110.8747   $110.87   $110.85   $110.90  
  Purchase #6 $150.67   12.298%   $169.1994   $169.20   $169.20   $169.20  
  Purchase #7 $42.74   8.554%   $46.396   $46.40   $46.40   $46.40  
  7 purchase totals = $973.21       $1,052.3415   $1,052.34   $1,052.30   $1,052.30