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 $208.61   6.386%   $221.9318   $221.93   $221.95   $221.90  
  Purchase #2 $212.27   10.490%   $234.5371   $234.54   $234.55   $234.50  
  Purchase #3 $189.95   8.764%   $206.5972   $206.60   $206.60   $206.60  
  Purchase #4 $211.86   7.388%   $227.5122   $227.51   $227.50   $227.50  
  Purchase #5 $26.44   12.812%   $29.8275   $29.83   $29.85   $29.80  
  Purchase #6 $227.31   5.412%   $239.612   $239.61   $239.60   $239.60  
  Purchase #7 $86.35   7.280%   $92.6363   $92.64   $92.65   $92.60  
  7 purchase totals = $1,162.79       $1,252.6541   $1,252.66   $1,252.70   $1,252.50