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 $168.78   8.279%   $182.7533   $182.75   $182.75   $182.80  
  Purchase #2 $178.74   3.494%   $184.9852   $184.99   $185.00   $185.00  
  Purchase #3 $158.36   6.651%   $168.8925   $168.89   $168.90   $168.90  
  Purchase #4 $70.59   6.271%   $75.0167   $75.02   $75.00   $75.00  
  Purchase #5 $210.76   13.578%   $239.377   $239.38   $239.40   $239.40  
  Purchase #6 $166.54   11.254%   $185.2824   $185.28   $185.30   $185.30  
  Purchase #7 $39.51   3.627%   $40.943   $40.94   $40.95   $40.90  
  7 purchase totals = $993.28       $1,077.2501   $1,077.25   $1,077.30   $1,077.30