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 $249.33   5.153%   $262.178   $262.18   $262.20   $262.20  
  Purchase #2 $209.27   13.416%   $237.3457   $237.35   $237.35   $237.30  
  Purchase #3 $153.65   8.407%   $166.5674   $166.57   $166.55   $166.60  
  Purchase #4 $235.30   6.395%   $250.3474   $250.35   $250.35   $250.30  
  Purchase #5 $8.85   4.744%   $9.2698   $9.27   $9.25   $9.30  
  Purchase #6 $113.90   6.473%   $121.2727   $121.27   $121.25   $121.30  
  Purchase #7 $159.92   5.610%   $168.8915   $168.89   $168.90   $168.90  
  7 purchase totals = $1,130.22       $1,215.8725   $1,215.88   $1,215.85   $1,215.90