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 $94.65   4.312%   $98.7313   $98.73   $98.75   $98.70  
  Purchase #2 $24.86   6.256%   $26.4152   $26.42   $26.40   $26.40  
  Purchase #3 $231.65   11.178%   $257.5438   $257.54   $257.55   $257.50  
  Purchase #4 $208.39   6.359%   $221.6415   $221.64   $221.65   $221.60  
  Purchase #5 $217.32   5.855%   $230.0441   $230.04   $230.05   $230.00  
  Purchase #6 $201.64   10.744%   $223.3042   $223.30   $223.30   $223.30  
  Purchase #7 $86.38   8.858%   $94.0315   $94.03   $94.05   $94.00  
  7 purchase totals = $1,064.89       $1,151.7116   $1,151.70   $1,151.75   $1,151.50