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	$70.78	11.575%	$78.9728	$78.97	$78.95	$79.00
Purchase #2	$223.87	4.223%	$233.324	$233.32	$233.30	$233.30
Purchase #3	$58.82	9.594%	$64.4632	$64.46	$64.45	$64.50
Purchase #4	$79.94	11.429%	$89.0763	$89.08	$89.10	$89.10
Purchase #5	$43.74	10.838%	$48.4805	$48.48	$48.50	$48.50
Purchase #6	$45.73	9.436%	$50.0451	$50.05	$50.05	$50.00
Purchase #7	$11.43	6.599%	$12.1843	$12.18	$12.20	$12.20
7 purchase totals =	$534.31		$576.5462	$576.54	$576.55	$576.60