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 $249.84   10.181%   $275.2762   $275.28   $275.30   $275.30  
  Purchase #2 $244.99   12.816%   $276.3879   $276.39   $276.40   $276.40  
  Purchase #3 $157.28   3.592%   $162.9295   $162.93   $162.95   $162.90  
  Purchase #4 $228.60   11.411%   $254.6855   $254.69   $254.70   $254.70  
  Purchase #5 $195.60   9.722%   $214.6162   $214.62   $214.60   $214.60  
  Purchase #6 $231.29   10.457%   $255.476   $255.48   $255.50   $255.50  
  Purchase #7 $225.99   7.470%   $242.8715   $242.87   $242.85   $242.90  
  7 purchase totals = $1,533.59       $1,682.2428   $1,682.26   $1,682.30   $1,682.30