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 $195.54   5.657%   $206.6017   $206.60   $206.60   $206.60  
  Purchase #2 $76.69   6.451%   $81.6373   $81.64   $81.65   $81.60  
  Purchase #3 $76.65   4.196%   $79.8662   $79.87   $79.85   $79.90  
  Purchase #4 $58.83   9.178%   $64.2294   $64.23   $64.25   $64.20  
  Purchase #5 $65.70   8.802%   $71.4829   $71.48   $71.50   $71.50  
  Purchase #6 $55.31   12.594%   $62.2757   $62.28   $62.30   $62.30  
  Purchase #7 $6.57   7.122%   $7.0379   $7.04   $7.05   $7.00  
  7 purchase totals = $535.29       $573.1311   $573.14   $573.20   $573.10