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	$223.51	4.851%	$234.3525	$234.35	$234.35	$234.40
Purchase #2	$86.62	3.639%	$89.7721	$89.77	$89.75	$89.80
Purchase #3	$234.58	12.103%	$262.9712	$262.97	$262.95	$263.00
Purchase #4	$51.45	6.132%	$54.6049	$54.60	$54.60	$54.60
Purchase #5	$77.36	4.177%	$80.5913	$80.59	$80.60	$80.60
Purchase #6	$101.36	10.198%	$111.6967	$111.70	$111.70	$111.70
Purchase #7	$6.93	9.690%	$7.6015	$7.60	$7.60	$7.60
7 purchase totals =	$781.81		$841.5902	$841.58	$841.55	$841.70