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 $109.84   6.285%   $116.7434   $116.74   $116.75   $116.70  
  Purchase #2 $70.98   6.154%   $75.3481   $75.35   $75.35   $75.30  
  Purchase #3 $94.70   8.139%   $102.4076   $102.41   $102.40   $102.40  
  Purchase #4 $117.66   12.475%   $132.3381   $132.34   $132.35   $132.30  
  Purchase #5 $236.91   10.675%   $262.2001   $262.20   $262.20   $262.20  
  Purchase #6 $90.45   4.810%   $94.8006   $94.80   $94.80   $94.80  
  Purchase #7 $161.36   6.314%   $171.5483   $171.55   $171.55   $171.50  
  7 purchase totals = $881.90       $955.3862   $955.39   $955.40   $955.20