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 $246.57   8.225%   $266.8504   $266.85   $266.85   $266.90  
  Purchase #2 $87.65   6.791%   $93.6023   $93.60   $93.60   $93.60  
  Purchase #3 $162.45   13.116%   $183.7569   $183.76   $183.75   $183.80  
  Purchase #4 $19.70   11.458%   $21.9572   $21.96   $21.95   $22.00  
  Purchase #5 $192.64   13.473%   $218.5944   $218.59   $218.60   $218.60  
  Purchase #6 $106.40   8.294%   $115.2248   $115.22   $115.20   $115.20  
  Purchase #7 $5.61   5.755%   $5.9329   $5.93   $5.95   $5.90  
  7 purchase totals = $821.02       $905.9189   $905.91   $905.90   $906.00