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	$38.68	12.412%	$43.481	$43.48	$43.50	$43.50
Purchase #2	$54.37	13.469%	$61.6931	$61.69	$61.70	$61.70
Purchase #3	$48.55	11.617%	$54.1901	$54.19	$54.20	$54.20
Purchase #4	$39.64	12.335%	$44.5296	$44.53	$44.55	$44.50
Purchase #5	$225.52	12.622%	$253.9851	$253.99	$254.00	$254.00
Purchase #6	$98.67	13.156%	$111.651	$111.65	$111.65	$111.70
Purchase #7	$99.79	9.495%	$109.2651	$109.27	$109.25	$109.30
7 purchase totals =	$605.22		$678.7950	$678.80	$678.85	$678.90