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 $185.44   4.677%   $194.113   $194.11   $194.10   $194.10  
  Purchase #2 $122.72   10.366%   $135.4412   $135.44   $135.45   $135.40  
  Purchase #3 $159.94   8.451%   $173.4565   $173.46   $173.45   $173.50  
  Purchase #4 $31.98   10.794%   $35.4319   $35.43   $35.45   $35.40  
  Purchase #5 $10.30   6.291%   $10.948   $10.95   $10.95   $10.90  
  Purchase #6 $180.49   13.311%   $204.515   $204.52   $204.50   $204.50  
  Purchase #7 $222.32   9.137%   $242.6334   $242.63   $242.65   $242.60  
  7 purchase totals = $913.19       $996.5390   $996.54   $996.55   $996.40