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 $57.51   8.754%   $62.5444   $62.54   $62.55   $62.50  
  Purchase #2 $91.73   7.759%   $98.8473   $98.85   $98.85   $98.80  
  Purchase #3 $33.33   5.407%   $35.1322   $35.13   $35.15   $35.10  
  Purchase #4 $98.42   8.127%   $106.4186   $106.42   $106.40   $106.40  
  Purchase #5 $150.92   4.207%   $157.2692   $157.27   $157.25   $157.30  
  Purchase #6 $36.47   5.511%   $38.4799   $38.48   $38.50   $38.50  
  Purchase #7 $185.51   11.448%   $206.7472   $206.75   $206.75   $206.70  
  7 purchase totals = $653.89       $705.4388   $705.44   $705.45   $705.30