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 $234.90   10.762%   $260.1799   $260.18   $260.20   $260.20  
  Purchase #2 $66.85   13.455%   $75.8447   $75.84   $75.85   $75.80  
  Purchase #3 $166.70   9.383%   $182.3415   $182.34   $182.35   $182.30  
  Purchase #4 $8.46   12.545%   $9.5213   $9.52   $9.50   $9.50  
  Purchase #5 $80.25   8.302%   $86.9124   $86.91   $86.90   $86.90  
  Purchase #6 $93.46   4.433%   $97.6031   $97.60   $97.60   $97.60  
  Purchase #7 $238.33   10.386%   $263.083   $263.08   $263.10   $263.10  
  7 purchase totals = $888.95       $975.4859   $975.47   $975.50   $975.40