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 $54.70   13.831%   $62.2656   $62.27   $62.25   $62.30  
  Purchase #2 $56.41   7.692%   $60.7491   $60.75   $60.75   $60.70  
  Purchase #3 $24.77   5.263%   $26.0736   $26.07   $26.05   $26.10  
  Purchase #4 $233.74   3.341%   $241.5493   $241.55   $241.55   $241.50  
  Purchase #5 $110.70   4.838%   $116.0557   $116.06   $116.05   $116.10  
  Purchase #6 $31.56   3.255%   $32.5873   $32.59   $32.60   $32.60  
  Purchase #7 $164.25   13.544%   $186.496   $186.50   $186.50   $186.50  
  7 purchase totals = $676.13       $725.7766   $725.79   $725.75   $725.80