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 $245.26   8.680%   $266.5486   $266.55   $266.55   $266.50  
  Purchase #2 $220.87   10.485%   $244.0282   $244.03   $244.05   $244.00  
  Purchase #3 $101.76   7.437%   $109.3279   $109.33   $109.35   $109.30  
  Purchase #4 $177.94   10.701%   $196.9814   $196.98   $197.00   $197.00  
  Purchase #5 $105.42   10.328%   $116.3078   $116.31   $116.30   $116.30  
  Purchase #6 $77.43   12.703%   $87.2659   $87.27   $87.25   $87.30  
  Purchase #7 $231.82   10.195%   $255.454   $255.45   $255.45   $255.50  
  7 purchase totals = $1,160.50       $1,275.9138   $1,275.92   $1,275.95   $1,275.90