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 $113.51   11.482%   $126.5432   $126.54   $126.55   $126.50  
  Purchase #2 $174.73   4.600%   $182.7676   $182.77   $182.75   $182.80  
  Purchase #3 $11.75   9.343%   $12.8478   $12.85   $12.85   $12.80  
  Purchase #4 $191.58   11.226%   $213.0868   $213.09   $213.10   $213.10  
  Purchase #5 $151.72   13.690%   $172.4905   $172.49   $172.50   $172.50  
  Purchase #6 $144.87   9.397%   $158.4834   $158.48   $158.50   $158.50  
  Purchase #7 $192.42   5.302%   $202.6221   $202.62   $202.60   $202.60  
  7 purchase totals = $980.58       $1,068.8414   $1,068.84   $1,068.85   $1,068.80