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 $233.98   13.809%   $266.2903   $266.29   $266.30   $266.30  
  Purchase #2 $9.28   4.678%   $9.7141   $9.71   $9.70   $9.70  
  Purchase #3 $147.44   7.282%   $158.1766   $158.18   $158.20   $158.20  
  Purchase #4 $174.40   13.216%   $197.4487   $197.45   $197.45   $197.40  
  Purchase #5 $245.65   6.528%   $261.686   $261.69   $261.70   $261.70  
  Purchase #6 $57.25   3.793%   $59.4215   $59.42   $59.40   $59.40  
  Purchase #7 $201.89   5.289%   $212.568   $212.57   $212.55   $212.60  
  7 purchase totals = $1,069.89       $1,165.3052   $1,165.31   $1,165.30   $1,165.30