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	$207.88	6.594%	$221.5876	$221.59	$221.60	$221.60
Purchase #2	$206.70	12.489%	$232.5148	$232.51	$232.50	$232.50
Purchase #3	$99.87	6.778%	$106.6392	$106.64	$106.65	$106.60
Purchase #4	$58.38	12.413%	$65.6267	$65.63	$65.65	$65.60
Purchase #5	$102.81	8.223%	$111.2641	$111.26	$111.25	$111.30
Purchase #6	$41.33	11.681%	$46.1578	$46.16	$46.15	$46.20
Purchase #7	$39.96	7.183%	$42.8303	$42.83	$42.85	$42.80
7 purchase totals =	$756.93		$826.6205	$826.62	$826.65	$826.60