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 $61.72   10.211%   $68.0222   $68.02   $68.00   $68.00  
  Purchase #2 $175.31   7.733%   $188.8667   $188.87   $188.85   $188.90  
  Purchase #3 $197.28   3.537%   $204.2578   $204.26   $204.25   $204.30  
  Purchase #4 $127.51   13.703%   $144.9827   $144.98   $145.00   $145.00  
  Purchase #5 $98.42   4.716%   $103.0615   $103.06   $103.05   $103.10  
  Purchase #6 $169.62   5.824%   $179.4987   $179.50   $179.50   $179.50  
  Purchase #7 $106.60   9.697%   $116.937   $116.94   $116.95   $116.90  
  7 purchase totals = $936.46       $1,005.6266   $1,005.63   $1,005.60   $1,005.70