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 $58.33   8.190%   $63.1072   $63.11   $63.10   $63.10  
  Purchase #2 $34.31   3.684%   $35.574   $35.57   $35.55   $35.60  
  Purchase #3 $93.36   3.501%   $96.6285   $96.63   $96.65   $96.60  
  Purchase #4 $79.87   7.390%   $85.7724   $85.77   $85.75   $85.80  
  Purchase #5 $229.47   5.699%   $242.5475   $242.55   $242.55   $242.50  
  Purchase #6 $14.92   6.473%   $15.8858   $15.89   $15.90   $15.90  
  Purchase #7 $237.52   11.766%   $265.4666   $265.47   $265.45   $265.50  
  7 purchase totals = $747.78       $804.9820   $804.99   $804.95   $805.00