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 $197.35   4.687%   $206.5998   $206.60   $206.60   $206.60  
  Purchase #2 $89.56   9.431%   $98.0064   $98.01   $98.00   $98.00  
  Purchase #3 $50.97   4.495%   $53.2611   $53.26   $53.25   $53.30  
  Purchase #4 $169.85   12.597%   $191.246   $191.25   $191.25   $191.20  
  Purchase #5 $230.76   6.589%   $245.9648   $245.96   $245.95   $246.00  
  Purchase #6 $243.96   3.296%   $252.0009   $252.00   $252.00   $252.00  
  Purchase #7 $184.37   13.339%   $208.9631   $208.96   $208.95   $209.00  
  7 purchase totals = $1,166.82       $1,256.0421   $1,256.04   $1,256.00   $1,256.10