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	$17.37	5.182%	$18.2701	$18.27	$18.25	$18.30
Purchase #2	$112.73	5.513%	$118.9448	$118.94	$118.95	$118.90
Purchase #3	$249.33	12.184%	$279.7084	$279.71	$279.70	$279.70
Purchase #4	$196.35	6.671%	$209.4485	$209.45	$209.45	$209.40
Purchase #5	$101.86	7.588%	$109.5891	$109.59	$109.60	$109.60
Purchase #6	$228.50	7.145%	$244.8263	$244.83	$244.85	$244.80
Purchase #7	$58.72	9.790%	$64.4687	$64.47	$64.45	$64.50
7 purchase totals =	$964.86		$1,045.2559	$1,045.26	$1,045.25	$1,045.20