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	$52.52	9.474%	$57.4957	$57.50	$57.50	$57.50
Purchase #2	$174.60	9.343%	$190.9129	$190.91	$190.90	$190.90
Purchase #3	$116.61	13.401%	$132.2369	$132.24	$132.25	$132.20
Purchase #4	$214.91	6.810%	$229.5454	$229.55	$229.55	$229.50
Purchase #5	$128.64	12.731%	$145.0172	$145.02	$145.00	$145.00
Purchase #6	$123.64	10.179%	$136.2253	$136.23	$136.25	$136.20
Purchase #7	$125.37	4.713%	$131.2787	$131.28	$131.30	$131.30
7 purchase totals =	$936.29		$1,022.7121	$1,022.73	$1,022.75	$1,022.60