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 $163.95   13.146%   $185.5029   $185.50   $185.50   $185.50  
  Purchase #2 $75.83   10.190%   $83.5571   $83.56   $83.55   $83.60  
  Purchase #3 $243.42   7.105%   $260.715   $260.72   $260.70   $260.70  
  Purchase #4 $43.78   7.401%   $47.0202   $47.02   $47.00   $47.00  
  Purchase #5 $115.46   8.826%   $125.6505   $125.65   $125.65   $125.70  
  Purchase #6 $5.27   11.223%   $5.8615   $5.86   $5.85   $5.90  
  Purchase #7 $241.28   5.857%   $255.4118   $255.41   $255.40   $255.40  
  7 purchase totals = $888.99       $963.7190   $963.72   $963.65   $963.80