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	$19.57	10.417%	$21.6086	$21.61	$21.60	$21.60
Purchase #2	$112.49	13.204%	$127.3432	$127.34	$127.35	$127.30
Purchase #3	$105.45	5.470%	$111.2181	$111.22	$111.20	$111.20
Purchase #4	$88.61	8.668%	$96.2907	$96.29	$96.30	$96.30
Purchase #5	$195.89	13.639%	$222.6074	$222.61	$222.60	$222.60
Purchase #6	$111.52	3.723%	$115.6719	$115.67	$115.65	$115.70
Purchase #7	$120.78	6.156%	$128.2152	$128.22	$128.20	$128.20
7 purchase totals =	$754.31		$822.9551	$822.96	$822.90	$822.90