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 $219.26   13.678%   $249.2504   $249.25   $249.25   $249.30  
  Purchase #2 $203.33   5.221%   $213.9459   $213.95   $213.95   $213.90  
  Purchase #3 $37.90   4.568%   $39.6313   $39.63   $39.65   $39.60  
  Purchase #4 $159.36   8.413%   $172.767   $172.77   $172.75   $172.80  
  Purchase #5 $188.79   9.806%   $207.3027   $207.30   $207.30   $207.30  
  Purchase #6 $230.45   9.733%   $252.8797   $252.88   $252.90   $252.90  
  Purchase #7 $204.38   13.327%   $231.6177   $231.62   $231.60   $231.60  
  7 purchase totals = $1,243.47       $1,367.3947   $1,367.40   $1,367.40   $1,367.40