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 $86.65   10.327%   $95.5983   $95.60   $95.60   $95.60  
  Purchase #2 $214.65   11.587%   $239.5215   $239.52   $239.50   $239.50  
  Purchase #3 $139.28   7.158%   $149.2497   $149.25   $149.25   $149.20  
  Purchase #4 $66.88   9.361%   $73.1406   $73.14   $73.15   $73.10  
  Purchase #5 $112.63   3.748%   $116.8514   $116.85   $116.85   $116.90  
  Purchase #6 $247.97   13.376%   $281.1385   $281.14   $281.15   $281.10  
  Purchase #7 $40.40   7.549%   $43.4498   $43.45   $43.45   $43.40  
  7 purchase totals = $908.46       $998.9498   $998.95   $998.95   $998.80