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 $248.28   3.594%   $257.2032   $257.20   $257.20   $257.20  
  Purchase #2 $85.68   13.190%   $96.9812   $96.98   $97.00   $97.00  
  Purchase #3 $138.78   12.339%   $155.9041   $155.90   $155.90   $155.90  
  Purchase #4 $164.44   5.627%   $173.693   $173.69   $173.70   $173.70  
  Purchase #5 $241.84   4.848%   $253.5644   $253.56   $253.55   $253.60  
  Purchase #6 $208.45   10.426%   $230.183   $230.18   $230.20   $230.20  
  Purchase #7 $175.94   12.607%   $198.1208   $198.12   $198.10   $198.10  
  7 purchase totals = $1,263.41       $1,365.6497   $1,365.63   $1,365.65   $1,365.70