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	$79.82	12.366%	$89.6905	$89.69	$89.70	$89.70
Purchase #2	$30.40	5.563%	$32.0912	$32.09	$32.10	$32.10
Purchase #3	$42.93	11.597%	$47.9086	$47.91	$47.90	$47.90
Purchase #4	$188.49	11.575%	$210.3077	$210.31	$210.30	$210.30
Purchase #5	$201.68	13.177%	$228.2554	$228.26	$228.25	$228.30
Purchase #6	$96.42	8.338%	$104.4595	$104.46	$104.45	$104.50
Purchase #7	$51.94	3.682%	$53.8524	$53.85	$53.85	$53.90
7 purchase totals =	$691.68		$766.5653	$766.57	$766.55	$766.70