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	$29.60	9.760%	$32.489	$32.49	$32.50	$32.50
Purchase #2	$158.52	8.625%	$172.1924	$172.19	$172.20	$172.20
Purchase #3	$239.85	6.529%	$255.5098	$255.51	$255.50	$255.50
Purchase #4	$161.43	9.284%	$176.4172	$176.42	$176.40	$176.40
Purchase #5	$135.46	13.853%	$154.2253	$154.23	$154.25	$154.20
Purchase #6	$250.90	9.199%	$273.9803	$273.98	$274.00	$274.00
Purchase #7	$42.25	5.768%	$44.687	$44.69	$44.70	$44.70
7 purchase totals =	$1,018.01		$1,109.5010	$1,109.51	$1,109.55	$1,109.50