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	$238.90	8.433%	$259.0464	$259.05	$259.05	$259.00
Purchase #2	$83.81	6.516%	$89.2711	$89.27	$89.25	$89.30
Purchase #3	$55.61	12.564%	$62.5968	$62.60	$62.60	$62.60
Purchase #4	$226.89	4.341%	$236.7393	$236.74	$236.75	$236.70
Purchase #5	$204.42	3.163%	$210.8858	$210.89	$210.90	$210.90
Purchase #6	$98.80	4.559%	$103.3043	$103.30	$103.30	$103.30
Purchase #7	$9.45	6.844%	$10.0968	$10.10	$10.10	$10.10
7 purchase totals =	$917.88		$971.9405	$971.95	$971.95	$971.90