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 $78.79   9.456%   $86.2404   $86.24   $86.25   $86.20  
  Purchase #2 $238.61   6.169%   $253.3299   $253.33   $253.35   $253.30  
  Purchase #3 $235.96   11.551%   $263.2157   $263.22   $263.20   $263.20  
  Purchase #4 $207.38   7.505%   $222.9439   $222.94   $222.95   $222.90  
  Purchase #5 $197.28   8.696%   $214.4355   $214.44   $214.45   $214.40  
  Purchase #6 $236.94   4.131%   $246.728   $246.73   $246.75   $246.70  
  Purchase #7 $147.63   6.644%   $157.4385   $157.44   $157.45   $157.40  
  7 purchase totals = $1,342.59       $1,444.3319   $1,444.34   $1,444.40   $1,444.10