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 $59.87   4.604%   $62.6264   $62.63   $62.65   $62.60  
  Purchase #2 $65.93   6.134%   $69.9741   $69.97   $69.95   $70.00  
  Purchase #3 $92.80   6.526%   $98.8561   $98.86   $98.85   $98.90  
  Purchase #4 $51.39   5.512%   $54.2226   $54.22   $54.20   $54.20  
  Purchase #5 $66.29   5.222%   $69.7517   $69.75   $69.75   $69.80  
  Purchase #6 $168.88   6.559%   $179.9568   $179.96   $179.95   $180.00  
  Purchase #7 $14.98   12.481%   $16.8497   $16.85   $16.85   $16.80  
  7 purchase totals = $520.14       $552.2374   $552.24   $552.20   $552.30