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 $41.95   10.632%   $46.4101   $46.41   $46.40   $46.40  
  Purchase #2 $113.74   5.833%   $120.3745   $120.37   $120.35   $120.40  
  Purchase #3 $73.33   10.794%   $81.2452   $81.25   $81.25   $81.20  
  Purchase #4 $47.77   8.534%   $51.8467   $51.85   $51.85   $51.80  
  Purchase #5 $116.66   9.114%   $127.2924   $127.29   $127.30   $127.30  
  Purchase #6 $77.56   4.728%   $81.227   $81.23   $81.25   $81.20  
  Purchase #7 $219.47   11.459%   $244.6191   $244.62   $244.60   $244.60  
  7 purchase totals = $690.48       $753.0150   $753.02   $753.00   $752.90