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 $56.72   6.161%   $60.2145   $60.21   $60.20   $60.20  
  Purchase #2 $150.45   6.856%   $160.7649   $160.76   $160.75   $160.80  
  Purchase #3 $208.54   7.564%   $224.314   $224.31   $224.30   $224.30  
  Purchase #4 $83.81   8.265%   $90.7369   $90.74   $90.75   $90.70  
  Purchase #5 $62.44   4.844%   $65.4646   $65.46   $65.45   $65.50  
  Purchase #6 $179.84   13.370%   $203.8846   $203.88   $203.90   $203.90  
  Purchase #7 $66.50   7.833%   $71.7089   $71.71   $71.70   $71.70  
  7 purchase totals = $808.30       $877.0884   $877.07   $877.05   $877.10