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 $184.76   4.347%   $192.7915   $192.79   $192.80   $192.80  
  Purchase #2 $165.55   10.864%   $183.5354   $183.54   $183.55   $183.50  
  Purchase #3 $96.90   3.606%   $100.3942   $100.39   $100.40   $100.40  
  Purchase #4 $157.99   10.557%   $174.669   $174.67   $174.65   $174.70  
  Purchase #5 $137.41   6.222%   $145.9597   $145.96   $145.95   $146.00  
  Purchase #6 $223.40   11.624%   $249.368   $249.37   $249.35   $249.40  
  Purchase #7 $189.47   13.766%   $215.5524   $215.55   $215.55   $215.60  
  7 purchase totals = $1,155.48       $1,262.2702   $1,262.27   $1,262.25   $1,262.40