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 $58.37   3.111%   $60.1859   $60.19   $60.20   $60.20  
  Purchase #2 $99.93   3.729%   $103.6564   $103.66   $103.65   $103.70  
  Purchase #3 $137.41   12.176%   $154.141   $154.14   $154.15   $154.10  
  Purchase #4 $60.37   9.758%   $66.2609   $66.26   $66.25   $66.30  
  Purchase #5 $9.49   9.182%   $10.3614   $10.36   $10.35   $10.40  
  Purchase #6 $163.81   11.849%   $183.2198   $183.22   $183.20   $183.20  
  Purchase #7 $165.45   7.125%   $177.2383   $177.24   $177.25   $177.20  
  7 purchase totals = $694.83       $755.0637   $755.07   $755.05   $755.10