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 $55.81   6.598%   $59.4923   $59.49   $59.50   $59.50  
  Purchase #2 $243.81   8.554%   $264.6655   $264.67   $264.65   $264.70  
  Purchase #3 $94.37   13.786%   $107.3798   $107.38   $107.40   $107.40  
  Purchase #4 $222.66   9.698%   $244.2536   $244.25   $244.25   $244.30  
  Purchase #5 $170.35   5.104%   $179.0447   $179.04   $179.05   $179.00  
  Purchase #6 $101.54   13.730%   $115.4814   $115.48   $115.50   $115.50  
  Purchase #7 $203.33   4.729%   $212.9455   $212.95   $212.95   $212.90  
  7 purchase totals = $1,091.87       $1,183.2628   $1,183.26   $1,183.30   $1,183.30