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 $246.85   5.770%   $261.0932   $261.09   $261.10   $261.10  
  Purchase #2 $92.53   6.295%   $98.3548   $98.35   $98.35   $98.40  
  Purchase #3 $203.75   3.727%   $211.3438   $211.34   $211.35   $211.30  
  Purchase #4 $239.33   7.351%   $256.9231   $256.92   $256.90   $256.90  
  Purchase #5 $55.50   4.642%   $58.0763   $58.08   $58.10   $58.10  
  Purchase #6 $123.26   10.683%   $136.4279   $136.43   $136.45   $136.40  
  Purchase #7 $154.63   6.249%   $164.2928   $164.29   $164.30   $164.30  
  7 purchase totals = $1,115.85       $1,186.5119   $1,186.50   $1,186.55   $1,186.50