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 $134.59   11.190%   $149.6506   $149.65   $149.65   $149.70  
  Purchase #2 $85.88   11.170%   $95.4728   $95.47   $95.45   $95.50  
  Purchase #3 $154.43   6.429%   $164.3583   $164.36   $164.35   $164.40  
  Purchase #4 $75.93   10.310%   $83.7584   $83.76   $83.75   $83.80  
  Purchase #5 $102.92   12.472%   $115.7562   $115.76   $115.75   $115.80  
  Purchase #6 $176.49   10.571%   $195.1468   $195.15   $195.15   $195.10  
  Purchase #7 $25.83   7.634%   $27.8019   $27.80   $27.80   $27.80  
  7 purchase totals = $756.07       $831.9450   $831.95   $831.90   $832.10