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 $218.62   13.109%   $247.2789   $247.28   $247.30   $247.30  
  Purchase #2 $189.88   11.579%   $211.8662   $211.87   $211.85   $211.90  
  Purchase #3 $117.74   8.647%   $127.921   $127.92   $127.90   $127.90  
  Purchase #4 $214.34   3.473%   $221.784   $221.78   $221.80   $221.80  
  Purchase #5 $62.97   12.401%   $70.7789   $70.78   $70.80   $70.80  
  Purchase #6 $22.97   11.514%   $25.6148   $25.61   $25.60   $25.60  
  Purchase #7 $190.92   12.116%   $214.0519   $214.05   $214.05   $214.10  
  7 purchase totals = $1,017.44       $1,119.2957   $1,119.29   $1,119.30   $1,119.40