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 $93.29   8.563%   $101.2784   $101.28   $101.30   $101.30  
  Purchase #2 $90.27   5.676%   $95.3937   $95.39   $95.40   $95.40  
  Purchase #3 $168.47   3.142%   $173.7633   $173.76   $173.75   $173.80  
  Purchase #4 $36.91   4.514%   $38.5761   $38.58   $38.60   $38.60  
  Purchase #5 $27.39   11.470%   $30.5316   $30.53   $30.55   $30.50  
  Purchase #6 $38.58   5.103%   $40.5487   $40.55   $40.55   $40.50  
  Purchase #7 $248.51   4.222%   $259.0021   $259.00   $259.00   $259.00  
  7 purchase totals = $703.42       $739.0939   $739.09   $739.15   $739.10