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 $73.37   12.615%   $82.6256   $82.63   $82.65   $82.60  
  Purchase #2 $218.40   8.458%   $236.8723   $236.87   $236.85   $236.90  
  Purchase #3 $240.35   12.222%   $269.7256   $269.73   $269.75   $269.70  
  Purchase #4 $69.97   13.312%   $79.2844   $79.28   $79.30   $79.30  
  Purchase #5 $109.36   7.632%   $117.7064   $117.71   $117.70   $117.70  
  Purchase #6 $214.97   4.102%   $223.7881   $223.79   $223.80   $223.80  
  Purchase #7 $62.35   6.310%   $66.2843   $66.28   $66.30   $66.30  
  7 purchase totals = $988.77       $1,076.2867   $1,076.29   $1,076.35   $1,076.30