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 $32.68   8.523%   $35.4653   $35.47   $35.45   $35.50  
  Purchase #2 $165.33   11.847%   $184.9166   $184.92   $184.90   $184.90  
  Purchase #3 $64.84   6.619%   $69.1318   $69.13   $69.15   $69.10  
  Purchase #4 $93.42   3.115%   $96.33   $96.33   $96.35   $96.30  
  Purchase #5 $153.65   10.187%   $169.3023   $169.30   $169.30   $169.30  
  Purchase #6 $60.62   6.176%   $64.3639   $64.36   $64.35   $64.40  
  Purchase #7 $94.68   3.605%   $98.0932   $98.09   $98.10   $98.10  
  7 purchase totals = $665.22       $717.6031   $717.60   $717.60   $717.60