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 $68.61   3.859%   $71.2577   $71.26   $71.25   $71.30  
  Purchase #2 $143.41   6.134%   $152.2068   $152.21   $152.20   $152.20  
  Purchase #3 $62.77   4.581%   $65.6455   $65.65   $65.65   $65.60  
  Purchase #4 $71.90   3.240%   $74.2296   $74.23   $74.25   $74.20  
  Purchase #5 $171.81   10.643%   $190.0957   $190.10   $190.10   $190.10  
  Purchase #6 $217.52   11.646%   $242.8524   $242.85   $242.85   $242.90  
  Purchase #7 $178.44   11.663%   $199.2515   $199.25   $199.25   $199.30  
  7 purchase totals = $914.46       $995.5392   $995.55   $995.55   $995.60