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 $49.85   13.844%   $56.7512   $56.75   $56.75   $56.80  
  Purchase #2 $157.37   7.553%   $169.2562   $169.26   $169.25   $169.30  
  Purchase #3 $80.83   8.617%   $87.7951   $87.80   $87.80   $87.80  
  Purchase #4 $98.41   13.344%   $111.5418   $111.54   $111.55   $111.50  
  Purchase #5 $104.35   11.343%   $116.1864   $116.19   $116.20   $116.20  
  Purchase #6 $142.88   12.730%   $161.0686   $161.07   $161.05   $161.10  
  Purchase #7 $8.64   10.262%   $9.5266   $9.53   $9.55   $9.50  
  7 purchase totals = $642.33       $712.1259   $712.14   $712.15   $712.20