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 $233.33   8.763%   $253.7767   $253.78   $253.80   $253.80  
  Purchase #2 $248.59   11.728%   $277.7446   $277.74   $277.75   $277.70  
  Purchase #3 $112.84   13.660%   $128.2539   $128.25   $128.25   $128.30  
  Purchase #4 $44.56   4.149%   $46.4088   $46.41   $46.40   $46.40  
  Purchase #5 $100.98   8.871%   $109.9379   $109.94   $109.95   $109.90  
  Purchase #6 $208.46   11.854%   $233.1708   $233.17   $233.15   $233.20  
  Purchase #7 $80.33   4.569%   $84.0003   $84.00   $84.00   $84.00  
  7 purchase totals = $1,029.09       $1,133.2930   $1,133.29   $1,133.30   $1,133.30