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	$230.25	8.545%	$249.9249	$249.92	$249.90	$249.90
Purchase #2	$56.56	4.356%	$59.0238	$59.02	$59.00	$59.00
Purchase #3	$18.33	10.679%	$20.2875	$20.29	$20.30	$20.30
Purchase #4	$175.69	13.556%	$199.5065	$199.51	$199.50	$199.50
Purchase #5	$48.34	11.219%	$53.7633	$53.76	$53.75	$53.80
Purchase #6	$21.34	10.313%	$23.5408	$23.54	$23.55	$23.50
Purchase #7	$183.73	4.292%	$191.6157	$191.62	$191.60	$191.60
7 purchase totals =	$734.24		$797.6625	$797.66	$797.60	$797.60