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 $149.27   6.854%   $159.501   $159.50   $159.50   $159.50  
  Purchase #2 $70.34   8.523%   $76.3351   $76.34   $76.35   $76.30  
  Purchase #3 $205.91   10.727%   $227.998   $228.00   $228.00   $228.00  
  Purchase #4 $18.49   11.250%   $20.5701   $20.57   $20.55   $20.60  
  Purchase #5 $44.78   11.658%   $50.0005   $50.00   $50.00   $50.00  
  Purchase #6 $115.40   6.487%   $122.886   $122.89   $122.90   $122.90  
  Purchase #7 $164.82   5.759%   $174.312   $174.31   $174.30   $174.30  
  7 purchase totals = $769.01       $831.6027   $831.61   $831.60   $831.60