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 $46.85   7.419%   $50.3258   $50.33   $50.35   $50.30  
  Purchase #2 $82.75   3.146%   $85.3533   $85.35   $85.35   $85.40  
  Purchase #3 $229.87   5.843%   $243.3013   $243.30   $243.30   $243.30  
  Purchase #4 $70.38   8.424%   $76.3088   $76.31   $76.30   $76.30  
  Purchase #5 $116.62   6.373%   $124.0522   $124.05   $124.05   $124.10  
  Purchase #6 $238.98   6.821%   $255.2808   $255.28   $255.30   $255.30  
  Purchase #7 $16.79   10.294%   $18.5184   $18.52   $18.50   $18.50  
  7 purchase totals = $802.24       $853.1406   $853.14   $853.15   $853.20