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	$32.52	10.623%	$35.9746	$35.97	$35.95	$36.00
Purchase #2	$131.25	10.137%	$144.5548	$144.55	$144.55	$144.60
Purchase #3	$39.86	9.455%	$43.6288	$43.63	$43.65	$43.60
Purchase #4	$143.27	6.519%	$152.6098	$152.61	$152.60	$152.60
Purchase #5	$5.93	6.356%	$6.3069	$6.31	$6.30	$6.30
Purchase #6	$8.99	8.113%	$9.7194	$9.72	$9.70	$9.70
Purchase #7	$188.30	4.359%	$196.508	$196.51	$196.50	$196.50
7 purchase totals =	$550.12		$589.3023	$589.30	$589.25	$589.30