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 $98.58   5.680%   $104.1793   $104.18   $104.20   $104.20  
  Purchase #2 $150.75   4.305%   $157.2398   $157.24   $157.25   $157.20  
  Purchase #3 $112.93   3.763%   $117.1796   $117.18   $117.20   $117.20  
  Purchase #4 $16.85   4.404%   $17.5921   $17.59   $17.60   $17.60  
  Purchase #5 $83.85   12.266%   $94.135   $94.14   $94.15   $94.10  
  Purchase #6 $207.37   12.307%   $232.891   $232.89   $232.90   $232.90  
  Purchase #7 $216.41   7.164%   $231.9136   $231.91   $231.90   $231.90  
  7 purchase totals = $886.74       $955.1304   $955.13   $955.20   $955.10