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	$54.45	8.498%	$59.0772	$59.08	$59.10	$59.10
Purchase #2	$118.68	4.298%	$123.7809	$123.78	$123.80	$123.80
Purchase #3	$118.31	7.719%	$127.4423	$127.44	$127.45	$127.40
Purchase #4	$145.33	4.699%	$152.1591	$152.16	$152.15	$152.20
Purchase #5	$36.78	11.672%	$41.073	$41.07	$41.05	$41.10
Purchase #6	$166.27	13.150%	$188.1345	$188.13	$188.15	$188.10
Purchase #7	$134.76	8.426%	$146.1149	$146.11	$146.10	$146.10
7 purchase totals =	$774.58		$837.7819	$837.77	$837.80	$837.80