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	$17.61	5.862%	$18.6423	$18.64	$18.65	$18.60
Purchase #2	$40.89	7.503%	$43.958	$43.96	$43.95	$44.00
Purchase #3	$124.34	9.635%	$136.3202	$136.32	$136.30	$136.30
Purchase #4	$107.48	5.289%	$113.1646	$113.16	$113.15	$113.20
Purchase #5	$123.85	3.461%	$128.1364	$128.14	$128.15	$128.10
Purchase #6	$225.43	13.292%	$255.3942	$255.39	$255.40	$255.40
Purchase #7	$100.57	13.414%	$114.0605	$114.06	$114.05	$114.10
7 purchase totals =	$740.17		$809.6762	$809.67	$809.65	$809.70