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	$58.32	10.443%	$64.4104	$64.41	$64.40	$64.40
Purchase #2	$181.60	5.604%	$191.7769	$191.78	$191.80	$191.80
Purchase #3	$100.56	12.103%	$112.7308	$112.73	$112.75	$112.70
Purchase #4	$73.86	11.444%	$82.3125	$82.31	$82.30	$82.30
Purchase #5	$98.68	11.103%	$109.6364	$109.64	$109.65	$109.60
Purchase #6	$111.29	10.722%	$123.2225	$123.22	$123.20	$123.20
Purchase #7	$121.48	11.734%	$135.7345	$135.73	$135.75	$135.70
7 purchase totals =	$745.79		$819.8240	$819.82	$819.85	$819.70