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	$20.69	5.172%	$21.7601	$21.76	$21.75	$21.80
Purchase #2	$40.91	6.355%	$43.5098	$43.51	$43.50	$43.50
Purchase #3	$63.86	5.679%	$67.4866	$67.49	$67.50	$67.50
Purchase #4	$19.65	9.764%	$21.5686	$21.57	$21.55	$21.60
Purchase #5	$12.78	10.394%	$14.1084	$14.11	$14.10	$14.10
Purchase #6	$134.67	12.776%	$151.8754	$151.88	$151.90	$151.90
Purchase #7	$100.35	5.300%	$105.6686	$105.67	$105.65	$105.70
7 purchase totals =	$392.91		$425.9775	$425.99	$425.95	$426.10