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	$51.63	13.378%	$58.5371	$58.54	$58.55	$58.50
Purchase #2	$46.48	3.551%	$48.1305	$48.13	$48.15	$48.10
Purchase #3	$105.91	8.108%	$114.4972	$114.50	$114.50	$114.50
Purchase #4	$139.99	10.283%	$154.3852	$154.39	$154.40	$154.40
Purchase #5	$145.87	13.417%	$165.4414	$165.44	$165.45	$165.40
Purchase #6	$177.65	4.637%	$185.8876	$185.89	$185.90	$185.90
Purchase #7	$99.79	3.791%	$103.573	$103.57	$103.55	$103.60
7 purchase totals =	$767.32		$830.4520	$830.46	$830.50	$830.40