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 $202.35   6.505%   $215.5129   $215.51   $215.50   $215.50  
  Purchase #2 $146.26   9.649%   $160.3726   $160.37   $160.35   $160.40  
  Purchase #3 $22.28   4.824%   $23.3548   $23.35   $23.35   $23.40  
  Purchase #4 $212.79   5.224%   $223.9061   $223.91   $223.90   $223.90  
  Purchase #5 $81.71   8.511%   $88.6643   $88.66   $88.65   $88.70  
  Purchase #6 $131.63   8.139%   $142.3434   $142.34   $142.35   $142.30  
  Purchase #7 $154.49   8.539%   $167.6819   $167.68   $167.70   $167.70  
  7 purchase totals = $951.51       $1,021.8360   $1,021.82   $1,021.80   $1,021.90