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 $24.58   5.378%   $25.9019   $25.90   $25.90   $25.90  
  Purchase #2 $223.86   3.502%   $231.6996   $231.70   $231.70   $231.70  
  Purchase #3 $176.36   5.650%   $186.3243   $186.32   $186.30   $186.30  
  Purchase #4 $21.57   8.497%   $23.4028   $23.40   $23.40   $23.40  
  Purchase #5 $110.69   3.198%   $114.2299   $114.23   $114.25   $114.20  
  Purchase #6 $95.50   9.469%   $104.5429   $104.54   $104.55   $104.50  
  Purchase #7 $207.56   9.771%   $227.8407   $227.84   $227.85   $227.80  
  7 purchase totals = $860.12       $913.9421   $913.93   $913.95   $913.80