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	$51.72	7.181%	$55.434	$55.43	$55.45	$55.40
Purchase #2	$126.60	5.316%	$133.3301	$133.33	$133.35	$133.30
Purchase #3	$82.32	12.865%	$92.9105	$92.91	$92.90	$92.90
Purchase #4	$215.78	13.691%	$245.3224	$245.32	$245.30	$245.30
Purchase #5	$105.64	4.426%	$110.3156	$110.32	$110.30	$110.30
Purchase #6	$98.31	3.167%	$101.4235	$101.42	$101.40	$101.40
Purchase #7	$154.46	12.554%	$173.8509	$173.85	$173.85	$173.90
7 purchase totals =	$834.83		$912.5870	$912.58	$912.55	$912.50