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	$69.41	11.307%	$77.2582	$77.26	$77.25	$77.30
Purchase #2	$240.94	11.680%	$269.0818	$269.08	$269.10	$269.10
Purchase #3	$30.96	4.147%	$32.2439	$32.24	$32.25	$32.20
Purchase #4	$81.25	13.424%	$92.157	$92.16	$92.15	$92.20
Purchase #5	$129.35	10.761%	$143.2694	$143.27	$143.25	$143.30
Purchase #6	$88.32	11.258%	$98.2631	$98.26	$98.25	$98.30
Purchase #7	$27.72	7.629%	$29.8348	$29.83	$29.85	$29.80
7 purchase totals =	$667.95		$742.1082	$742.10	$742.10	$742.20