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	$212.62	13.679%	$241.7043	$241.70	$241.70	$241.70
Purchase #2	$189.52	3.731%	$196.591	$196.59	$196.60	$196.60
Purchase #3	$144.72	11.827%	$161.836	$161.84	$161.85	$161.80
Purchase #4	$70.48	3.644%	$73.0483	$73.05	$73.05	$73.00
Purchase #5	$190.41	6.851%	$203.455	$203.46	$203.45	$203.50
Purchase #6	$50.58	13.219%	$57.2662	$57.27	$57.25	$57.30
Purchase #7	$76.79	8.596%	$83.3909	$83.39	$83.40	$83.40
7 purchase totals =	$935.12		$1,017.2917	$1,017.30	$1,017.30	$1,017.30