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 $24.44   3.586%   $25.3164   $25.32   $25.30   $25.30  
  Purchase #2 $227.41   10.693%   $251.727   $251.73   $251.75   $251.70  
  Purchase #3 $192.67   12.439%   $216.6362   $216.64   $216.65   $216.60  
  Purchase #4 $122.27   3.448%   $126.4859   $126.49   $126.50   $126.50  
  Purchase #5 $245.33   3.121%   $252.9867   $252.99   $253.00   $253.00  
  Purchase #6 $87.42   11.118%   $97.1394   $97.14   $97.15   $97.10  
  Purchase #7 $248.98   10.115%   $274.1643   $274.16   $274.15   $274.20  
  7 purchase totals = $1,148.52       $1,244.4559   $1,244.47   $1,244.50   $1,244.40