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 $219.97   8.748%   $239.213   $239.21   $239.20   $239.20  
  Purchase #2 $91.73   10.693%   $101.5387   $101.54   $101.55   $101.50  
  Purchase #3 $156.44   4.459%   $163.4157   $163.42   $163.40   $163.40  
  Purchase #4 $180.49   8.239%   $195.3606   $195.36   $195.35   $195.40  
  Purchase #5 $239.41   9.695%   $262.6208   $262.62   $262.60   $262.60  
  Purchase #6 $152.94   4.673%   $160.0869   $160.09   $160.10   $160.10  
  Purchase #7 $120.55   5.345%   $126.9934   $126.99   $127.00   $127.00  
  7 purchase totals = $1,161.53       $1,249.2291   $1,249.23   $1,249.20   $1,249.20