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 $223.94   11.409%   $249.4893   $249.49   $249.50   $249.50  
  Purchase #2 $177.87   4.345%   $185.5985   $185.60   $185.60   $185.60  
  Purchase #3 $250.41   3.268%   $258.5934   $258.59   $258.60   $258.60  
  Purchase #4 $92.56   3.194%   $95.5164   $95.52   $95.50   $95.50  
  Purchase #5 $218.81   9.665%   $239.958   $239.96   $239.95   $240.00  
  Purchase #6 $146.85   11.816%   $164.2018   $164.20   $164.20   $164.20  
  Purchase #7 $154.30   8.365%   $167.2072   $167.21   $167.20   $167.20  
  7 purchase totals = $1,264.74       $1,360.5646   $1,360.57   $1,360.55   $1,360.60