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 $246.66   9.203%   $269.3601   $269.36   $269.35   $269.40  
  Purchase #2 $188.91   12.841%   $213.1679   $213.17   $213.15   $213.20  
  Purchase #3 $227.39   7.261%   $243.9008   $243.90   $243.90   $243.90  
  Purchase #4 $65.67   12.114%   $73.6253   $73.63   $73.65   $73.60  
  Purchase #5 $214.85   5.171%   $225.9599   $225.96   $225.95   $226.00  
  Purchase #6 $145.41   6.307%   $154.581   $154.58   $154.60   $154.60  
  Purchase #7 $220.54   12.782%   $248.7294   $248.73   $248.75   $248.70  
  7 purchase totals = $1,309.43       $1,429.3244   $1,429.33   $1,429.35   $1,429.40