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	$39.83	7.171%	$42.6862	$42.69	$42.70	$42.70
Purchase #2	$11.64	7.634%	$12.5286	$12.53	$12.55	$12.50
Purchase #3	$229.82	5.424%	$242.2854	$242.29	$242.30	$242.30
Purchase #4	$131.79	4.705%	$137.9907	$137.99	$138.00	$138.00
Purchase #5	$98.39	13.405%	$111.5792	$111.58	$111.60	$111.60
Purchase #6	$146.40	8.300%	$158.5512	$158.55	$158.55	$158.60
Purchase #7	$65.71	3.429%	$67.9632	$67.96	$67.95	$68.00
7 purchase totals =	$723.58		$773.5845	$773.59	$773.65	$773.70