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	$57.32	9.750%	$62.9087	$62.91	$62.90	$62.90
Purchase #2	$85.60	5.426%	$90.2447	$90.24	$90.25	$90.20
Purchase #3	$217.76	5.712%	$230.1985	$230.20	$230.20	$230.20
Purchase #4	$35.84	5.838%	$37.9323	$37.93	$37.95	$37.90
Purchase #5	$84.59	7.653%	$91.0637	$91.06	$91.05	$91.10
Purchase #6	$20.93	4.549%	$21.8821	$21.88	$21.90	$21.90
Purchase #7	$18.46	9.255%	$20.1685	$20.17	$20.15	$20.20
7 purchase totals =	$520.50		$554.3985	$554.39	$554.40	$554.40