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 $89.75   6.483%   $95.5685   $95.57   $95.55   $95.60  
  Purchase #2 $200.39   8.770%   $217.9642   $217.96   $217.95   $218.00  
  Purchase #3 $6.47   5.561%   $6.8298   $6.83   $6.85   $6.80  
  Purchase #4 $119.63   3.191%   $123.4474   $123.45   $123.45   $123.40  
  Purchase #5 $70.33   7.318%   $75.4767   $75.48   $75.50   $75.50  
  Purchase #6 $56.28   10.613%   $62.253   $62.25   $62.25   $62.30  
  Purchase #7 $185.84   3.480%   $192.3072   $192.31   $192.30   $192.30  
  7 purchase totals = $728.69       $773.8468   $773.85   $773.85   $773.90