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 $246.97   6.329%   $262.6007   $262.60   $262.60   $262.60  
  Purchase #2 $119.60   6.783%   $127.7125   $127.71   $127.70   $127.70  
  Purchase #3 $41.44   11.721%   $46.2972   $46.30   $46.30   $46.30  
  Purchase #4 $191.39   11.688%   $213.7597   $213.76   $213.75   $213.80  
  Purchase #5 $244.88   9.416%   $267.9379   $267.94   $267.95   $267.90  
  Purchase #6 $19.89   5.345%   $20.9531   $20.95   $20.95   $21.00  
  Purchase #7 $176.97   8.852%   $192.6354   $192.64   $192.65   $192.60  
  7 purchase totals = $1,041.14       $1,131.8965   $1,131.90   $1,131.90   $1,131.90