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	$249.99	9.295%	$273.2266	$273.23	$273.25	$273.20
Purchase #2	$75.85	3.192%	$78.2711	$78.27	$78.25	$78.30
Purchase #3	$100.87	4.747%	$105.6583	$105.66	$105.65	$105.70
Purchase #4	$53.76	5.525%	$56.7302	$56.73	$56.75	$56.70
Purchase #5	$43.45	9.302%	$47.4917	$47.49	$47.50	$47.50
Purchase #6	$213.49	11.752%	$238.5793	$238.58	$238.60	$238.60
Purchase #7	$236.99	5.559%	$250.1643	$250.16	$250.15	$250.20
7 purchase totals =	$974.40		$1,050.1215	$1,050.12	$1,050.15	$1,050.20