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 $174.73   3.266%   $180.4367   $180.44   $180.45   $180.40  
  Purchase #2 $206.90   4.112%   $215.4077   $215.41   $215.40   $215.40  
  Purchase #3 $36.52   4.872%   $38.2993   $38.30   $38.30   $38.30  
  Purchase #4 $197.62   8.794%   $214.9987   $215.00   $215.00   $215.00  
  Purchase #5 $125.55   11.821%   $140.3913   $140.39   $140.40   $140.40  
  Purchase #6 $103.41   8.383%   $112.0789   $112.08   $112.10   $112.10  
  Purchase #7 $244.58   12.343%   $274.7685   $274.77   $274.75   $274.80  
  7 purchase totals = $1,089.31       $1,176.3811   $1,176.39   $1,176.40   $1,176.40