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	$39.95	5.177%	$42.0182	$42.02	$42.00	$42.00
Purchase #2	$243.56	11.848%	$272.417	$272.42	$272.40	$272.40
Purchase #3	$167.46	7.335%	$179.7432	$179.74	$179.75	$179.70
Purchase #4	$226.34	13.250%	$256.3301	$256.33	$256.35	$256.30
Purchase #5	$186.42	3.790%	$193.4853	$193.49	$193.50	$193.50
Purchase #6	$196.26	6.704%	$209.4173	$209.42	$209.40	$209.40
Purchase #7	$111.46	13.616%	$126.6364	$126.64	$126.65	$126.60
7 purchase totals =	$1,171.45		$1,280.0475	$1,280.06	$1,280.05	$1,279.90