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 $247.26   8.858%   $269.1623   $269.16   $269.15   $269.20  
  Purchase #2 $234.69   3.511%   $242.93   $242.93   $242.95   $242.90  
  Purchase #3 $67.43   8.617%   $73.2404   $73.24   $73.25   $73.20  
  Purchase #4 $204.74   13.334%   $232.04   $232.04   $232.05   $232.00  
  Purchase #5 $212.88   11.251%   $236.8311   $236.83   $236.85   $236.80  
  Purchase #6 $104.42   12.243%   $117.2041   $117.20   $117.20   $117.20  
  Purchase #7 $232.96   8.188%   $252.0348   $252.03   $252.05   $252.00  
  7 purchase totals = $1,304.38       $1,423.4427   $1,423.43   $1,423.50   $1,423.30