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	$156.66	5.755%	$165.6758	$165.68	$165.70	$165.70
Purchase #2	$86.66	5.342%	$91.2894	$91.29	$91.30	$91.30
Purchase #3	$101.66	12.139%	$114.0005	$114.00	$114.00	$114.00
Purchase #4	$32.70	3.115%	$33.7186	$33.72	$33.70	$33.70
Purchase #5	$18.35	11.524%	$20.4647	$20.46	$20.45	$20.50
Purchase #6	$26.81	9.396%	$29.3291	$29.33	$29.35	$29.30
Purchase #7	$87.39	4.595%	$91.4056	$91.41	$91.40	$91.40
7 purchase totals =	$510.23		$545.8837	$545.89	$545.90	$545.90