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 $164.63   6.213%   $174.8585   $174.86   $174.85   $174.90  
  Purchase #2 $59.78   8.248%   $64.7107   $64.71   $64.70   $64.70  
  Purchase #3 $152.88   9.507%   $167.4143   $167.41   $167.40   $167.40  
  Purchase #4 $154.30   7.765%   $166.2814   $166.28   $166.30   $166.30  
  Purchase #5 $250.81   13.116%   $283.7062   $283.71   $283.70   $283.70  
  Purchase #6 $244.30   13.233%   $276.6282   $276.63   $276.65   $276.60  
  Purchase #7 $115.73   11.510%   $129.0505   $129.05   $129.05   $129.10  
  7 purchase totals = $1,142.43       $1,262.6498   $1,262.65   $1,262.65   $1,262.70