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	$229.97	13.831%	$261.7772	$261.78	$261.80	$261.80
Purchase #2	$124.71	9.226%	$136.2157	$136.22	$136.20	$136.20
Purchase #3	$153.85	13.475%	$174.5813	$174.58	$174.60	$174.60
Purchase #4	$139.66	13.425%	$158.4094	$158.41	$158.40	$158.40
Purchase #5	$230.68	6.432%	$245.5173	$245.52	$245.50	$245.50
Purchase #6	$60.48	11.740%	$67.5804	$67.58	$67.60	$67.60
Purchase #7	$39.71	10.233%	$43.7735	$43.77	$43.75	$43.80
7 purchase totals =	$979.06		$1,087.8548	$1,087.86	$1,087.85	$1,087.90