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	$61.84	6.233%	$65.6945	$65.69	$65.70	$65.70
Purchase #2	$35.75	5.471%	$37.7059	$37.71	$37.70	$37.70
Purchase #3	$222.58	11.596%	$248.3904	$248.39	$248.40	$248.40
Purchase #4	$89.31	11.342%	$99.4395	$99.44	$99.45	$99.40
Purchase #5	$127.30	3.431%	$131.6677	$131.67	$131.65	$131.70
Purchase #6	$123.75	13.734%	$140.7458	$140.75	$140.75	$140.70
Purchase #7	$112.73	9.645%	$123.6028	$123.60	$123.60	$123.60
7 purchase totals =	$773.26		$847.2466	$847.25	$847.25	$847.20