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 $66.61   3.451%   $68.9087   $68.91   $68.90   $68.90  
  Purchase #2 $192.99   5.284%   $203.1876   $203.19   $203.20   $203.20  
  Purchase #3 $19.46   4.711%   $20.3768   $20.38   $20.40   $20.40  
  Purchase #4 $93.39   6.198%   $99.1783   $99.18   $99.20   $99.20  
  Purchase #5 $127.26   9.199%   $138.9666   $138.97   $138.95   $139.00  
  Purchase #6 $53.64   6.211%   $56.9716   $56.97   $56.95   $57.00  
  Purchase #7 $35.25   3.848%   $36.6064   $36.61   $36.60   $36.60  
  7 purchase totals = $588.60       $624.1960   $624.21   $624.20   $624.30