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 $32.94   5.271%   $34.6763   $34.68   $34.70   $34.70  
  Purchase #2 $24.47   13.354%   $27.7377   $27.74   $27.75   $27.70  
  Purchase #3 $166.56   10.277%   $183.6774   $183.68   $183.70   $183.70  
  Purchase #4 $96.53   4.534%   $100.9067   $100.91   $100.90   $100.90  
  Purchase #5 $72.51   3.601%   $75.1211   $75.12   $75.10   $75.10  
  Purchase #6 $165.89   4.773%   $173.8079   $173.81   $173.80   $173.80  
  Purchase #7 $95.90   7.380%   $102.9774   $102.98   $103.00   $103.00  
  7 purchase totals = $654.80       $698.9045   $698.92   $698.95   $698.90