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	$48.32	13.587%	$54.8852	$54.89	$54.90	$54.90
Purchase #2	$227.50	7.612%	$244.8173	$244.82	$244.80	$244.80
Purchase #3	$147.27	5.317%	$155.1003	$155.10	$155.10	$155.10
Purchase #4	$139.72	7.553%	$150.2731	$150.27	$150.25	$150.30
Purchase #5	$122.74	3.757%	$127.3513	$127.35	$127.35	$127.40
Purchase #6	$83.85	9.552%	$91.8594	$91.86	$91.85	$91.90
Purchase #7	$189.89	7.254%	$203.6646	$203.66	$203.65	$203.70
7 purchase totals =	$959.29		$1,027.9512	$1,027.95	$1,027.90	$1,028.10