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 $86.86   8.234%   $94.0121   $94.01   $94.00   $94.00  
  Purchase #2 $188.39   6.207%   $200.0834   $200.08   $200.10   $200.10  
  Purchase #3 $220.57   8.187%   $238.6281   $238.63   $238.65   $238.60  
  Purchase #4 $83.69   11.153%   $93.0239   $93.02   $93.00   $93.00  
  Purchase #5 $125.72   10.787%   $139.2814   $139.28   $139.30   $139.30  
  Purchase #6 $136.78   8.813%   $148.8344   $148.83   $148.85   $148.80  
  Purchase #7 $71.65   8.126%   $77.4723   $77.47   $77.45   $77.50  
  7 purchase totals = $913.66       $991.3356   $991.32   $991.35   $991.30