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 $47.49   10.239%   $52.3525   $52.35   $52.35   $52.40  
  Purchase #2 $214.80   3.482%   $222.2793   $222.28   $222.30   $222.30  
  Purchase #3 $221.36   11.249%   $246.2608   $246.26   $246.25   $246.30  
  Purchase #4 $222.30   7.716%   $239.4527   $239.45   $239.45   $239.50  
  Purchase #5 $219.95   8.385%   $238.3928   $238.39   $238.40   $238.40  
  Purchase #6 $247.89   10.555%   $274.0548   $274.05   $274.05   $274.10  
  Purchase #7 $85.56   8.548%   $92.8737   $92.87   $92.85   $92.90  
  7 purchase totals = $1,259.35       $1,365.6666   $1,365.65   $1,365.65   $1,365.90