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 $118.64   11.816%   $132.6585   $132.66   $132.65   $132.70  
  Purchase #2 $34.99   3.791%   $36.3165   $36.32   $36.30   $36.30  
  Purchase #3 $20.73   10.591%   $22.9255   $22.93   $22.95   $22.90  
  Purchase #4 $234.91   3.229%   $242.4952   $242.50   $242.50   $242.50  
  Purchase #5 $204.42   10.636%   $226.1621   $226.16   $226.15   $226.20  
  Purchase #6 $96.61   8.368%   $104.6943   $104.69   $104.70   $104.70  
  Purchase #7 $93.39   3.744%   $96.8865   $96.89   $96.90   $96.90  
  7 purchase totals = $803.69       $862.1386   $862.15   $862.15   $862.20