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	$233.90	9.391%	$255.8655	$255.87	$255.85	$255.90
Purchase #2	$43.65	7.719%	$47.0193	$47.02	$47.00	$47.00
Purchase #3	$224.35	11.609%	$250.3948	$250.39	$250.40	$250.40
Purchase #4	$118.75	4.376%	$123.9465	$123.95	$123.95	$123.90
Purchase #5	$79.27	12.862%	$89.4657	$89.47	$89.45	$89.50
Purchase #6	$45.77	4.348%	$47.7601	$47.76	$47.75	$47.80
Purchase #7	$7.81	10.400%	$8.6222	$8.62	$8.60	$8.60
7 purchase totals =	$753.50		$823.0741	$823.08	$823.00	$823.10