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 $83.96   12.827%   $94.7295   $94.73   $94.75   $94.70  
  Purchase #2 $200.74   3.758%   $208.2838   $208.28   $208.30   $208.30  
  Purchase #3 $106.88   13.529%   $121.3398   $121.34   $121.35   $121.30  
  Purchase #4 $158.88   6.442%   $169.115   $169.12   $169.10   $169.10  
  Purchase #5 $76.96   10.292%   $84.8807   $84.88   $84.90   $84.90  
  Purchase #6 $236.94   3.328%   $244.8254   $244.83   $244.85   $244.80  
  Purchase #7 $93.33   13.260%   $105.7056   $105.71   $105.70   $105.70  
  7 purchase totals = $957.69       $1,028.8798   $1,028.89   $1,028.95   $1,028.80