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	$242.95	11.324%	$270.4617	$270.46	$270.45	$270.50
Purchase #2	$141.31	8.114%	$152.7759	$152.78	$152.80	$152.80
Purchase #3	$37.36	8.279%	$40.453	$40.45	$40.45	$40.50
Purchase #4	$56.25	10.265%	$62.0241	$62.02	$62.00	$62.00
Purchase #5	$127.35	3.545%	$131.8646	$131.86	$131.85	$131.90
Purchase #6	$26.42	7.321%	$28.3542	$28.35	$28.35	$28.40
Purchase #7	$183.99	11.858%	$205.8075	$205.81	$205.80	$205.80
7 purchase totals =	$815.63		$891.7410	$891.73	$891.70	$891.90