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 $201.48   6.213%   $213.998   $214.00   $214.00   $214.00  
  Purchase #2 $18.33   5.448%   $19.3286   $19.33   $19.35   $19.30  
  Purchase #3 $119.73   11.631%   $133.6558   $133.66   $133.65   $133.70  
  Purchase #4 $195.90   4.345%   $204.4119   $204.41   $204.40   $204.40  
  Purchase #5 $103.58   11.172%   $115.152   $115.15   $115.15   $115.20  
  Purchase #6 $19.55   9.189%   $21.3464   $21.35   $21.35   $21.30  
  Purchase #7 $30.89   11.227%   $34.358   $34.36   $34.35   $34.40  
  7 purchase totals = $689.46       $742.2507   $742.26   $742.25   $742.30