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	$91.33	8.871%	$99.4319	$99.43	$99.45	$99.40
Purchase #2	$120.95	13.408%	$137.167	$137.17	$137.15	$137.20
Purchase #3	$175.43	8.634%	$190.5766	$190.58	$190.60	$190.60
Purchase #4	$235.39	5.536%	$248.4212	$248.42	$248.40	$248.40
Purchase #5	$250.76	3.814%	$260.324	$260.32	$260.30	$260.30
Purchase #6	$166.58	8.127%	$180.118	$180.12	$180.10	$180.10
Purchase #7	$214.48	11.215%	$238.5339	$238.53	$238.55	$238.50
7 purchase totals =	$1,254.92		$1,354.5726	$1,354.57	$1,354.55	$1,354.50