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	$147.41	8.173%	$159.4578	$159.46	$159.45	$159.50
Purchase #2	$29.37	12.817%	$33.1344	$33.13	$33.15	$33.10
Purchase #3	$103.43	4.290%	$107.8671	$107.87	$107.85	$107.90
Purchase #4	$112.29	3.731%	$116.4795	$116.48	$116.50	$116.50
Purchase #5	$69.53	12.585%	$78.2804	$78.28	$78.30	$78.30
Purchase #6	$207.40	10.716%	$229.625	$229.63	$229.65	$229.60
Purchase #7	$61.27	4.666%	$64.1289	$64.13	$64.15	$64.10
7 purchase totals =	$730.70		$788.9731	$788.98	$789.05	$789.00