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	$19.74	10.548%	$21.8222	$21.82	$21.80	$21.80
Purchase #2	$61.95	6.262%	$65.8293	$65.83	$65.85	$65.80
Purchase #3	$165.59	7.599%	$178.1732	$178.17	$178.15	$178.20
Purchase #4	$64.30	11.124%	$71.4527	$71.45	$71.45	$71.50
Purchase #5	$200.77	6.298%	$213.4145	$213.41	$213.40	$213.40
Purchase #6	$228.90	9.208%	$249.9771	$249.98	$250.00	$250.00
Purchase #7	$248.88	11.678%	$277.9442	$277.94	$277.95	$277.90
7 purchase totals =	$990.13		$1,078.6132	$1,078.60	$1,078.60	$1,078.60