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 $211.63   12.603%   $238.3017   $238.30   $238.30   $238.30  
  Purchase #2 $88.93   8.250%   $96.2667   $96.27   $96.25   $96.30  
  Purchase #3 $76.36   5.214%   $80.3414   $80.34   $80.35   $80.30  
  Purchase #4 $184.26   6.784%   $196.7602   $196.76   $196.75   $196.80  
  Purchase #5 $174.82   10.665%   $193.4646   $193.46   $193.45   $193.50  
  Purchase #6 $207.34   3.850%   $215.3226   $215.32   $215.30   $215.30  
  Purchase #7 $198.86   3.548%   $205.9156   $205.92   $205.90   $205.90  
  7 purchase totals = $1,142.20       $1,226.3728   $1,226.37   $1,226.30   $1,226.40