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 $224.34   10.374%   $247.613   $247.61   $247.60   $247.60  
  Purchase #2 $53.39   3.515%   $55.2667   $55.27   $55.25   $55.30  
  Purchase #3 $202.48   13.864%   $230.5518   $230.55   $230.55   $230.60  
  Purchase #4 $72.40   5.127%   $76.1119   $76.11   $76.10   $76.10  
  Purchase #5 $125.54   4.185%   $130.7938   $130.79   $130.80   $130.80  
  Purchase #6 $73.88   4.234%   $77.0081   $77.01   $77.00   $77.00  
  Purchase #7 $116.70   4.216%   $121.6201   $121.62   $121.60   $121.60  
  7 purchase totals = $868.73       $938.9654   $938.96   $938.90   $939.00