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 $21.74   11.492%   $24.2384   $24.24   $24.25   $24.20  
  Purchase #2 $62.93   6.421%   $66.9707   $66.97   $66.95   $67.00  
  Purchase #3 $161.48   7.511%   $173.6088   $173.61   $173.60   $173.60  
  Purchase #4 $68.49   7.155%   $73.3905   $73.39   $73.40   $73.40  
  Purchase #5 $192.68   11.288%   $214.4297   $214.43   $214.45   $214.40  
  Purchase #6 $249.95   7.636%   $269.0362   $269.04   $269.05   $269.00  
  Purchase #7 $234.83   7.549%   $252.5573   $252.56   $252.55   $252.60  
  7 purchase totals = $992.10       $1,074.2316   $1,074.24   $1,074.25   $1,074.20