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 $71.42   3.435%   $73.8733   $73.87   $73.85   $73.90  
  Purchase #2 $194.47   13.108%   $219.9611   $219.96   $219.95   $220.00  
  Purchase #3 $187.31   9.783%   $205.6345   $205.63   $205.65   $205.60  
  Purchase #4 $207.33   8.377%   $224.698   $224.70   $224.70   $224.70  
  Purchase #5 $182.28   3.664%   $188.9587   $188.96   $188.95   $189.00  
  Purchase #6 $115.41   13.861%   $131.407   $131.41   $131.40   $131.40  
  Purchase #7 $250.81   3.219%   $258.8836   $258.88   $258.90   $258.90  
  7 purchase totals = $1,209.03       $1,303.4162   $1,303.41   $1,303.40   $1,303.50