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	$31.52	6.277%	$33.4985	$33.50	$33.50	$33.50
Purchase #2	$137.83	4.511%	$144.0475	$144.05	$144.05	$144.00
Purchase #3	$38.52	11.187%	$42.8292	$42.83	$42.85	$42.80
Purchase #4	$209.65	11.492%	$233.743	$233.74	$233.75	$233.70
Purchase #5	$13.62	9.630%	$14.9316	$14.93	$14.95	$14.90
Purchase #6	$55.79	6.662%	$59.5067	$59.51	$59.50	$59.50
Purchase #7	$8.87	13.593%	$10.0757	$10.08	$10.10	$10.10
7 purchase totals =	$495.80		$538.6322	$538.64	$538.70	$538.50