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 $114.48   8.324%   $124.0093   $124.01   $124.00   $124.00  
  Purchase #2 $38.46   6.461%   $40.9449   $40.94   $40.95   $40.90  
  Purchase #3 $123.69   5.597%   $130.6129   $130.61   $130.60   $130.60  
  Purchase #4 $230.60   9.659%   $252.8737   $252.87   $252.85   $252.90  
  Purchase #5 $50.38   9.843%   $55.3389   $55.34   $55.35   $55.30  
  Purchase #6 $209.88   11.160%   $233.3026   $233.30   $233.30   $233.30  
  Purchase #7 $173.69   5.268%   $182.84   $182.84   $182.85   $182.80  
  7 purchase totals = $941.18       $1,019.9223   $1,019.91   $1,019.90   $1,019.80