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 $110.93   8.118%   $119.9353   $119.94   $119.95   $119.90  
  Purchase #2 $194.63   4.272%   $202.9446   $202.94   $202.95   $202.90  
  Purchase #3 $38.62   9.508%   $42.292   $42.29   $42.30   $42.30  
  Purchase #4 $212.51   9.774%   $233.2807   $233.28   $233.30   $233.30  
  Purchase #5 $233.86   4.473%   $244.3206   $244.32   $244.30   $244.30  
  Purchase #6 $124.70   3.548%   $129.1244   $129.12   $129.10   $129.10  
  Purchase #7 $233.99   8.564%   $254.0289   $254.03   $254.05   $254.00  
  7 purchase totals = $1,149.24       $1,225.9265   $1,225.92   $1,225.95   $1,225.80