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 $242.75   6.383%   $258.2447   $258.24   $258.25   $258.20  
  Purchase #2 $185.27   3.544%   $191.836   $191.84   $191.85   $191.80  
  Purchase #3 $56.46   10.204%   $62.2212   $62.22   $62.20   $62.20  
  Purchase #4 $82.76   13.289%   $93.758   $93.76   $93.75   $93.80  
  Purchase #5 $60.93   12.454%   $68.5182   $68.52   $68.50   $68.50  
  Purchase #6 $163.46   3.238%   $168.7528   $168.75   $168.75   $168.80  
  Purchase #7 $163.62   3.828%   $169.8834   $169.88   $169.90   $169.90  
  7 purchase totals = $955.25       $1,013.2143   $1,013.21   $1,013.20   $1,013.20