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	$12.78	3.816%	$13.2677	$13.27	$13.25	$13.30
Purchase #2	$210.58	4.786%	$220.6584	$220.66	$220.65	$220.70
Purchase #3	$191.89	3.856%	$199.2893	$199.29	$199.30	$199.30
Purchase #4	$32.31	10.539%	$35.7152	$35.72	$35.70	$35.70
Purchase #5	$204.63	12.595%	$230.4031	$230.40	$230.40	$230.40
Purchase #6	$36.57	7.402%	$39.2769	$39.28	$39.30	$39.30
Purchase #7	$83.90	6.622%	$89.4559	$89.46	$89.45	$89.50
7 purchase totals =	$772.66		$828.0665	$828.08	$828.05	$828.20