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 $191.66   4.689%   $200.6469   $200.65   $200.65   $200.60  
  Purchase #2 $213.95   11.452%   $238.4516   $238.45   $238.45   $238.50  
  Purchase #3 $64.64   12.548%   $72.751   $72.75   $72.75   $72.80  
  Purchase #4 $98.66   11.706%   $110.2091   $110.21   $110.20   $110.20  
  Purchase #5 $22.90   5.213%   $24.0938   $24.09   $24.10   $24.10  
  Purchase #6 $169.44   8.710%   $184.1982   $184.20   $184.20   $184.20  
  Purchase #7 $133.99   13.636%   $152.2609   $152.26   $152.25   $152.30  
  7 purchase totals = $895.24       $982.6115   $982.61   $982.60   $982.70