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 $86.89   6.274%   $92.3415   $92.34   $92.35   $92.30  
  Purchase #2 $20.85   11.821%   $23.3147   $23.31   $23.30   $23.30  
  Purchase #3 $121.34   3.352%   $125.4073   $125.41   $125.40   $125.40  
  Purchase #4 $250.63   7.490%   $269.4022   $269.40   $269.40   $269.40  
  Purchase #5 $76.99   6.465%   $81.9674   $81.97   $81.95   $82.00  
  Purchase #6 $244.70   6.206%   $259.8861   $259.89   $259.90   $259.90  
  Purchase #7 $141.83   9.756%   $155.6669   $155.67   $155.65   $155.70  
  7 purchase totals = $943.23       $1,007.9861   $1,007.99   $1,007.95   $1,008.00