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 $246.57   8.571%   $267.7035   $267.70   $267.70   $267.70  
  Purchase #2 $188.49   4.575%   $197.1134   $197.11   $197.10   $197.10  
  Purchase #3 $217.37   5.486%   $229.2949   $229.29   $229.30   $229.30  
  Purchase #4 $104.39   11.458%   $116.351   $116.35   $116.35   $116.40  
  Purchase #5 $159.63   7.360%   $171.3788   $171.38   $171.40   $171.40  
  Purchase #6 $125.61   4.148%   $130.8203   $130.82   $130.80   $130.80  
  Purchase #7 $194.47   9.455%   $212.8571   $212.86   $212.85   $212.90  
  7 purchase totals = $1,236.53       $1,325.5190   $1,325.51   $1,325.50   $1,325.60