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 $119.32   6.202%   $126.7202   $126.72   $126.70   $126.70  
  Purchase #2 $199.92   8.647%   $217.2071   $217.21   $217.20   $217.20  
  Purchase #3 $80.30   9.637%   $88.0385   $88.04   $88.05   $88.00  
  Purchase #4 $107.93   13.743%   $122.7628   $122.76   $122.75   $122.80  
  Purchase #5 $114.29   4.674%   $119.6319   $119.63   $119.65   $119.60  
  Purchase #6 $66.73   9.465%   $73.046   $73.05   $73.05   $73.00  
  Purchase #7 $232.97   3.829%   $241.8904   $241.89   $241.90   $241.90  
  7 purchase totals = $921.46       $989.2969   $989.30   $989.30   $989.20