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	$57.52	6.243%	$61.111	$61.11	$61.10	$61.10
Purchase #2	$9.42	9.683%	$10.3321	$10.33	$10.35	$10.30
Purchase #3	$98.83	9.262%	$107.9836	$107.98	$108.00	$108.00
Purchase #4	$40.51	5.846%	$42.8782	$42.88	$42.90	$42.90
Purchase #5	$34.71	10.667%	$38.4125	$38.41	$38.40	$38.40
Purchase #6	$117.57	9.116%	$128.2877	$128.29	$128.30	$128.30
Purchase #7	$22.96	12.333%	$25.7917	$25.79	$25.80	$25.80
7 purchase totals =	$381.52		$414.7968	$414.79	$414.85	$414.80