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	$96.49	4.552%	$100.8822	$100.88	$100.90	$100.90
Purchase #2	$239.38	4.377%	$249.8577	$249.86	$249.85	$249.90
Purchase #3	$60.65	3.232%	$62.6102	$62.61	$62.60	$62.60
Purchase #4	$16.78	12.632%	$18.8996	$18.90	$18.90	$18.90
Purchase #5	$235.33	3.670%	$243.9666	$243.97	$243.95	$244.00
Purchase #6	$104.79	6.247%	$111.3362	$111.34	$111.35	$111.30
Purchase #7	$202.27	6.456%	$215.3286	$215.33	$215.35	$215.30
7 purchase totals =	$955.69		$1,002.8811	$1,002.89	$1,002.90	$1,002.90