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 $58.95   13.462%   $66.8858   $66.89   $66.90   $66.90  
  Purchase #2 $168.95   4.343%   $176.2875   $176.29   $176.30   $176.30  
  Purchase #3 $77.78   8.634%   $84.4955   $84.50   $84.50   $84.50  
  Purchase #4 $122.97   6.856%   $131.4008   $131.40   $131.40   $131.40  
  Purchase #5 $33.38   5.364%   $35.1705   $35.17   $35.15   $35.20  
  Purchase #6 $16.84   4.489%   $17.5959   $17.60   $17.60   $17.60  
  Purchase #7 $48.80   3.115%   $50.3201   $50.32   $50.30   $50.30  
  7 purchase totals = $527.67       $562.1561   $562.17   $562.15   $562.20