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 $58.84   8.661%   $63.9361   $63.94   $63.95   $63.90  
  Purchase #2 $248.99   11.153%   $276.7599   $276.76   $276.75   $276.80  
  Purchase #3 $223.98   10.835%   $248.2482   $248.25   $248.25   $248.20  
  Purchase #4 $40.51   12.874%   $45.7253   $45.73   $45.75   $45.70  
  Purchase #5 $176.96   3.825%   $183.7287   $183.73   $183.75   $183.70  
  Purchase #6 $187.50   9.287%   $204.9131   $204.91   $204.90   $204.90  
  Purchase #7 $185.40   8.110%   $200.4359   $200.44   $200.45   $200.40  
  7 purchase totals = $1,122.18       $1,223.7472   $1,223.76   $1,223.80   $1,223.60