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 $55.27   9.697%   $60.6295   $60.63   $60.65   $60.60  
  Purchase #2 $14.34   12.834%   $16.1804   $16.18   $16.20   $16.20  
  Purchase #3 $108.48   11.425%   $120.8738   $120.87   $120.85   $120.90  
  Purchase #4 $151.79   10.152%   $167.1997   $167.20   $167.20   $167.20  
  Purchase #5 $216.55   13.452%   $245.6803   $245.68   $245.70   $245.70  
  Purchase #6 $186.33   3.357%   $192.5851   $192.59   $192.60   $192.60  
  Purchase #7 $125.83   11.492%   $140.2904   $140.29   $140.30   $140.30  
  7 purchase totals = $858.59       $943.4392   $943.44   $943.50   $943.50