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 $248.77   4.422%   $259.7706   $259.77   $259.75   $259.80  
  Purchase #2 $119.70   8.289%   $129.6219   $129.62   $129.60   $129.60  
  Purchase #3 $5.53   9.575%   $6.0595   $6.06   $6.05   $6.10  
  Purchase #4 $247.93   11.557%   $276.5833   $276.58   $276.60   $276.60  
  Purchase #5 $203.65   3.446%   $210.6678   $210.67   $210.65   $210.70  
  Purchase #6 $115.49   3.687%   $119.7481   $119.75   $119.75   $119.70  
  Purchase #7 $61.80   3.156%   $63.7504   $63.75   $63.75   $63.80  
  7 purchase totals = $1,002.87       $1,066.2016   $1,066.20   $1,066.15   $1,066.30