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	$82.60	4.505%	$86.3211	$86.32	$86.30	$86.30
Purchase #2	$64.87	8.314%	$70.2633	$70.26	$70.25	$70.30
Purchase #3	$95.70	8.102%	$103.4536	$103.45	$103.45	$103.50
Purchase #4	$103.99	6.282%	$110.5227	$110.52	$110.50	$110.50
Purchase #5	$140.63	3.433%	$145.4578	$145.46	$145.45	$145.50
Purchase #6	$58.91	4.163%	$61.3624	$61.36	$61.35	$61.40
Purchase #7	$103.41	8.809%	$112.5194	$112.52	$112.50	$112.50
7 purchase totals =	$650.11		$689.9003	$689.89	$689.80	$690.00