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 $250.27   7.322%   $268.5948   $268.59   $268.60   $268.60  
  Purchase #2 $156.53   10.633%   $173.1738   $173.17   $173.15   $173.20  
  Purchase #3 $11.36   5.284%   $11.9603   $11.96   $11.95   $12.00  
  Purchase #4 $84.51   3.829%   $87.7459   $87.75   $87.75   $87.70  
  Purchase #5 $155.49   13.472%   $176.4376   $176.44   $176.45   $176.40  
  Purchase #6 $72.57   4.751%   $76.0178   $76.02   $76.00   $76.00  
  Purchase #7 $65.48   4.626%   $68.5091   $68.51   $68.50   $68.50  
  7 purchase totals = $796.21       $862.4393   $862.44   $862.40   $862.40