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	$50.90	12.771%	$57.4004	$57.40	$57.40	$57.40
Purchase #2	$75.60	3.719%	$78.4116	$78.41	$78.40	$78.40
Purchase #3	$37.93	13.133%	$42.9113	$42.91	$42.90	$42.90
Purchase #4	$106.85	12.843%	$120.5727	$120.57	$120.55	$120.60
Purchase #5	$10.27	3.159%	$10.5944	$10.59	$10.60	$10.60
Purchase #6	$165.94	6.687%	$177.0364	$177.04	$177.05	$177.00
Purchase #7	$33.92	4.116%	$35.3161	$35.32	$35.30	$35.30
7 purchase totals =	$481.41		$522.2429	$522.24	$522.20	$522.20