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	$210.43	3.411%	$217.6078	$217.61	$217.60	$217.60
Purchase #2	$131.55	10.470%	$145.3233	$145.32	$145.30	$145.30
Purchase #3	$40.66	13.801%	$46.2715	$46.27	$46.25	$46.30
Purchase #4	$143.86	10.269%	$158.633	$158.63	$158.65	$158.60
Purchase #5	$43.78	6.802%	$46.7579	$46.76	$46.75	$46.80
Purchase #6	$75.65	9.391%	$82.7543	$82.75	$82.75	$82.80
Purchase #7	$121.71	9.723%	$133.5439	$133.54	$133.55	$133.50
7 purchase totals =	$767.64		$830.8917	$830.88	$830.85	$830.90