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 $202.59   3.309%   $209.2937   $209.29   $209.30   $209.30  
  Purchase #2 $125.63   5.121%   $132.0635   $132.06   $132.05   $132.10  
  Purchase #3 $84.49   8.567%   $91.7283   $91.73   $91.75   $91.70  
  Purchase #4 $240.43   8.295%   $260.3737   $260.37   $260.35   $260.40  
  Purchase #5 $159.56   4.314%   $166.4434   $166.44   $166.45   $166.40  
  Purchase #6 $15.54   5.123%   $16.3361   $16.34   $16.35   $16.30  
  Purchase #7 $161.67   5.376%   $170.3614   $170.36   $170.35   $170.40  
  7 purchase totals = $989.91       $1,046.6001   $1,046.59   $1,046.60   $1,046.60