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 $184.32   12.480%   $207.3231   $207.32   $207.30   $207.30  
  Purchase #2 $240.95   8.476%   $261.3729   $261.37   $261.35   $261.40  
  Purchase #3 $194.61   10.477%   $214.9993   $215.00   $215.00   $215.00  
  Purchase #4 $124.51   9.813%   $136.7282   $136.73   $136.75   $136.70  
  Purchase #5 $120.93   3.238%   $124.8457   $124.85   $124.85   $124.80  
  Purchase #6 $110.77   6.634%   $118.1185   $118.12   $118.10   $118.10  
  Purchase #7 $11.26   12.254%   $12.6398   $12.64   $12.65   $12.60  
  7 purchase totals = $987.35       $1,076.0275   $1,076.03   $1,076.00   $1,075.90