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 $119.63   6.161%   $127.0004   $127.00   $127.00   $127.00  
  Purchase #2 $71.97   10.539%   $79.5549   $79.55   $79.55   $79.60  
  Purchase #3 $229.49   5.381%   $241.8389   $241.84   $241.85   $241.80  
  Purchase #4 $77.38   11.134%   $85.9955   $86.00   $86.00   $86.00  
  Purchase #5 $62.42   9.718%   $68.486   $68.49   $68.50   $68.50  
  Purchase #6 $20.44   9.558%   $22.3937   $22.39   $22.40   $22.40  
  Purchase #7 $8.34   13.253%   $9.4453   $9.45   $9.45   $9.40  
  7 purchase totals = $589.67       $634.7147   $634.72   $634.75   $634.70