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 $119.88   13.823%   $136.451   $136.45   $136.45   $136.50  
  Purchase #2 $13.44   4.516%   $14.047   $14.05   $14.05   $14.00  
  Purchase #3 $87.61   12.283%   $98.3711   $98.37   $98.35   $98.40  
  Purchase #4 $178.79   5.516%   $188.6521   $188.65   $188.65   $188.70  
  Purchase #5 $192.79   6.661%   $205.6317   $205.63   $205.65   $205.60  
  Purchase #6 $243.28   9.685%   $266.8417   $266.84   $266.85   $266.80  
  Purchase #7 $148.49   12.228%   $166.6474   $166.65   $166.65   $166.60  
  7 purchase totals = $984.28       $1,076.6420   $1,076.64   $1,076.65   $1,076.60