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	$106.91	3.602%	$110.7609	$110.76	$110.75	$110.80
Purchase #2	$185.90	9.260%	$203.1143	$203.11	$203.10	$203.10
Purchase #3	$204.69	9.698%	$224.5408	$224.54	$224.55	$224.50
Purchase #4	$168.39	5.707%	$178	$178.00	$178.00	$178.00
Purchase #5	$131.99	10.293%	$145.5757	$145.58	$145.60	$145.60
Purchase #6	$103.65	7.294%	$111.2102	$111.21	$111.20	$111.20
Purchase #7	$118.35	7.557%	$127.2937	$127.29	$127.30	$127.30
7 purchase totals =	$1,019.88		$1,100.4956	$1,100.49	$1,100.50	$1,100.50