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	$14.89	5.162%	$15.6586	$15.66	$15.65	$15.70
Purchase #2	$36.87	6.658%	$39.3248	$39.32	$39.30	$39.30
Purchase #3	$127.50	13.326%	$144.4907	$144.49	$144.50	$144.50
Purchase #4	$96.36	4.558%	$100.7521	$100.75	$100.75	$100.80
Purchase #5	$200.77	6.170%	$213.1575	$213.16	$213.15	$213.20
Purchase #6	$195.40	7.626%	$210.3012	$210.30	$210.30	$210.30
Purchase #7	$59.76	9.744%	$65.583	$65.58	$65.60	$65.60
7 purchase totals =	$731.55		$789.2679	$789.26	$789.25	$789.40