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 $219.60   11.346%   $244.5158   $244.52   $244.50   $244.50  
  Purchase #2 $151.57   10.585%   $167.6137   $167.61   $167.60   $167.60  
  Purchase #3 $166.40   9.722%   $182.5774   $182.58   $182.60   $182.60  
  Purchase #4 $110.91   6.774%   $118.423   $118.42   $118.40   $118.40  
  Purchase #5 $227.95   12.272%   $255.924   $255.92   $255.90   $255.90  
  Purchase #6 $170.60   3.578%   $176.7041   $176.70   $176.70   $176.70  
  Purchase #7 $131.64   6.757%   $140.5349   $140.53   $140.55   $140.50  
  7 purchase totals = $1,178.67       $1,286.2929   $1,286.28   $1,286.25   $1,286.20