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 $61.38   4.856%   $64.3606   $64.36   $64.35   $64.40  
  Purchase #2 $61.92   7.178%   $66.3646   $66.36   $66.35   $66.40  
  Purchase #3 $91.50   7.384%   $98.2564   $98.26   $98.25   $98.30  
  Purchase #4 $16.70   3.584%   $17.2985   $17.30   $17.30   $17.30  
  Purchase #5 $71.42   6.595%   $76.1301   $76.13   $76.15   $76.10  
  Purchase #6 $211.58   12.437%   $237.8942   $237.89   $237.90   $237.90  
  Purchase #7 $126.74   6.237%   $134.6448   $134.64   $134.65   $134.60  
  7 purchase totals = $641.24       $694.9492   $694.94   $694.95   $695.00