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	$82.74	7.586%	$89.0167	$89.02	$89.00	$89.00
Purchase #2	$91.77	8.602%	$99.6641	$99.66	$99.65	$99.70
Purchase #3	$141.54	4.518%	$147.9348	$147.93	$147.95	$147.90
Purchase #4	$16.62	13.665%	$18.8911	$18.89	$18.90	$18.90
Purchase #5	$235.75	9.316%	$257.7125	$257.71	$257.70	$257.70
Purchase #6	$206.70	3.729%	$214.4078	$214.41	$214.40	$214.40
Purchase #7	$242.95	6.377%	$258.4429	$258.44	$258.45	$258.40
7 purchase totals =	$1,018.07		$1,086.0699	$1,086.06	$1,086.05	$1,086.00