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	$10.46	10.745%	$11.5839	$11.58	$11.60	$11.60
Purchase #2	$137.90	4.607%	$144.2531	$144.25	$144.25	$144.30
Purchase #3	$10.69	4.839%	$11.2073	$11.21	$11.20	$11.20
Purchase #4	$154.77	10.667%	$171.2793	$171.28	$171.30	$171.30
Purchase #5	$40.79	3.247%	$42.1145	$42.11	$42.10	$42.10
Purchase #6	$244.69	4.265%	$255.126	$255.13	$255.15	$255.10
Purchase #7	$240.94	11.467%	$268.5686	$268.57	$268.55	$268.60
7 purchase totals =	$840.24		$904.1327	$904.13	$904.15	$904.20