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 $214.43   5.727%   $226.7104   $226.71   $226.70   $226.70  
  Purchase #2 $7.56   13.674%   $8.5938   $8.59   $8.60   $8.60  
  Purchase #3 $87.45   8.854%   $95.1928   $95.19   $95.20   $95.20  
  Purchase #4 $92.38   9.673%   $101.3159   $101.32   $101.30   $101.30  
  Purchase #5 $151.76   6.173%   $161.1281   $161.13   $161.15   $161.10  
  Purchase #6 $165.97   4.662%   $173.7075   $173.71   $173.70   $173.70  
  Purchase #7 $16.51   4.675%   $17.2818   $17.28   $17.30   $17.30  
  7 purchase totals = $736.06       $783.9303   $783.93   $783.95   $783.90