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 $183.51   12.804%   $207.0066   $207.01   $207.00   $207.00  
  Purchase #2 $245.75   5.699%   $259.7553   $259.76   $259.75   $259.80  
  Purchase #3 $237.64   11.227%   $264.3198   $264.32   $264.30   $264.30  
  Purchase #4 $26.84   8.420%   $29.0999   $29.10   $29.10   $29.10  
  Purchase #5 $157.71   13.444%   $178.9125   $178.91   $178.90   $178.90  
  Purchase #6 $206.92   6.857%   $221.1085   $221.11   $221.10   $221.10  
  Purchase #7 $168.80   5.769%   $178.5381   $178.54   $178.55   $178.50  
  7 purchase totals = $1,227.17       $1,338.7407   $1,338.75   $1,338.70   $1,338.70