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	$20.25	4.614%	$21.1843	$21.18	$21.20	$21.20
Purchase #2	$250.71	5.228%	$263.8171	$263.82	$263.80	$263.80
Purchase #3	$21.88	11.580%	$24.4137	$24.41	$24.40	$24.40
Purchase #4	$117.70	8.208%	$127.3608	$127.36	$127.35	$127.40
Purchase #5	$135.92	11.496%	$151.5454	$151.55	$151.55	$151.50
Purchase #6	$225.98	7.130%	$242.0924	$242.09	$242.10	$242.10
Purchase #7	$94.44	11.406%	$105.2118	$105.21	$105.20	$105.20
7 purchase totals =	$866.88		$935.6255	$935.62	$935.60	$935.60