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 $135.93   4.419%   $141.9367   $141.94   $141.95   $141.90  
  Purchase #2 $237.53   12.192%   $266.4897   $266.49   $266.50   $266.50  
  Purchase #3 $78.49   9.784%   $86.1695   $86.17   $86.15   $86.20  
  Purchase #4 $148.98   5.856%   $157.7043   $157.70   $157.70   $157.70  
  Purchase #5 $203.42   11.445%   $226.7014   $226.70   $226.70   $226.70  
  Purchase #6 $113.63   6.338%   $120.8319   $120.83   $120.85   $120.80  
  Purchase #7 $192.86   6.728%   $205.8356   $205.84   $205.85   $205.80  
  7 purchase totals = $1,110.84       $1,205.6691   $1,205.67   $1,205.70   $1,205.60