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 $228.30   5.833%   $241.6167   $241.62   $241.60   $241.60  
  Purchase #2 $50.48   12.711%   $56.8965   $56.90   $56.90   $56.90  
  Purchase #3 $61.35   5.821%   $64.9212   $64.92   $64.90   $64.90  
  Purchase #4 $172.77   5.501%   $182.2741   $182.27   $182.25   $182.30  
  Purchase #5 $100.26   3.169%   $103.4372   $103.44   $103.45   $103.40  
  Purchase #6 $69.33   9.680%   $76.0411   $76.04   $76.05   $76.00  
  Purchase #7 $140.57   5.713%   $148.6008   $148.60   $148.60   $148.60  
  7 purchase totals = $823.06       $873.7876   $873.79   $873.75   $873.70