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	$36.98	6.728%	$39.468	$39.47	$39.45	$39.50
Purchase #2	$238.99	11.432%	$266.3113	$266.31	$266.30	$266.30
Purchase #3	$78.52	6.481%	$83.6089	$83.61	$83.60	$83.60
Purchase #4	$191.71	9.612%	$210.1372	$210.14	$210.15	$210.10
Purchase #5	$39.94	3.579%	$41.3695	$41.37	$41.35	$41.40
Purchase #6	$51.49	11.662%	$57.4948	$57.49	$57.50	$57.50
Purchase #7	$75.31	3.807%	$78.1771	$78.18	$78.20	$78.20
7 purchase totals =	$712.94		$776.5668	$776.57	$776.55	$776.60