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	$33.45	11.771%	$37.3874	$37.39	$37.40	$37.40
Purchase #2	$51.97	3.350%	$53.711	$53.71	$53.70	$53.70
Purchase #3	$238.95	6.825%	$255.2583	$255.26	$255.25	$255.30
Purchase #4	$153.45	4.611%	$160.5256	$160.53	$160.55	$160.50
Purchase #5	$235.78	11.872%	$263.7718	$263.77	$263.75	$263.80
Purchase #6	$40.77	10.838%	$45.1887	$45.19	$45.20	$45.20
Purchase #7	$239.76	11.798%	$268.0469	$268.05	$268.05	$268.00
7 purchase totals =	$994.13		$1,083.8897	$1,083.90	$1,083.90	$1,083.90