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 $216.44   4.572%   $226.3356   $226.34   $226.35   $226.30  
  Purchase #2 $165.76   10.193%   $182.6559   $182.66   $182.65   $182.70  
  Purchase #3 $24.42   7.398%   $26.2266   $26.23   $26.25   $26.20  
  Purchase #4 $245.46   7.207%   $263.1503   $263.15   $263.15   $263.20  
  Purchase #5 $248.71   11.712%   $277.8389   $277.84   $277.85   $277.80  
  Purchase #6 $67.73   11.438%   $75.477   $75.48   $75.50   $75.50  
  Purchase #7 $151.31   10.784%   $167.6273   $167.63   $167.65   $167.60  
  7 purchase totals = $1,119.83       $1,219.3116   $1,219.33   $1,219.40   $1,219.30