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	$46.71	3.373%	$48.2855	$48.29	$48.30	$48.30
Purchase #2	$230.43	4.785%	$241.4561	$241.46	$241.45	$241.50
Purchase #3	$91.59	10.773%	$101.457	$101.46	$101.45	$101.50
Purchase #4	$175.51	4.516%	$183.436	$183.44	$183.45	$183.40
Purchase #5	$250.55	13.489%	$284.3467	$284.35	$284.35	$284.30
Purchase #6	$48.91	4.740%	$51.2283	$51.23	$51.25	$51.20
Purchase #7	$66.84	6.813%	$71.3938	$71.39	$71.40	$71.40
7 purchase totals =	$910.54		$981.6034	$981.62	$981.65	$981.60