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 $56.42   9.730%   $61.9097   $61.91   $61.90   $61.90  
  Purchase #2 $249.34   7.301%   $267.5443   $267.54   $267.55   $267.50  
  Purchase #3 $66.44   13.602%   $75.4772   $75.48   $75.50   $75.50  
  Purchase #4 $208.86   10.572%   $230.9407   $230.94   $230.95   $230.90  
  Purchase #5 $156.33   4.753%   $163.7604   $163.76   $163.75   $163.80  
  Purchase #6 $20.63   12.750%   $23.2603   $23.26   $23.25   $23.30  
  Purchase #7 $111.57   10.826%   $123.6486   $123.65   $123.65   $123.60  
  7 purchase totals = $869.59       $946.5412   $946.54   $946.55   $946.50