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 $202.97   10.773%   $224.836   $224.84   $224.85   $224.80  
  Purchase #2 $199.52   7.118%   $213.7218   $213.72   $213.70   $213.70  
  Purchase #3 $26.39   10.357%   $29.1232   $29.12   $29.10   $29.10  
  Purchase #4 $189.33   5.593%   $199.9192   $199.92   $199.90   $199.90  
  Purchase #5 $56.30   5.496%   $59.3942   $59.39   $59.40   $59.40  
  Purchase #6 $159.70   10.811%   $176.9652   $176.97   $176.95   $177.00  
  Purchase #7 $124.25   6.383%   $132.1809   $132.18   $132.20   $132.20  
  7 purchase totals = $958.46       $1,036.1405   $1,036.14   $1,036.10   $1,036.10