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 $14.56   11.605%   $16.2497   $16.25   $16.25   $16.20  
  Purchase #2 $179.41   12.664%   $202.1305   $202.13   $202.15   $202.10  
  Purchase #3 $214.53   9.179%   $234.2217   $234.22   $234.20   $234.20  
  Purchase #4 $142.43   10.640%   $157.5846   $157.58   $157.60   $157.60  
  Purchase #5 $234.43   4.207%   $244.2925   $244.29   $244.30   $244.30  
  Purchase #6 $218.36   10.164%   $240.5541   $240.55   $240.55   $240.60  
  Purchase #7 $170.91   7.433%   $183.6137   $183.61   $183.60   $183.60  
  7 purchase totals = $1,174.63       $1,278.6468   $1,278.63   $1,278.65   $1,278.60