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	$77.76	7.536%	$83.62	$83.62	$83.60	$83.60
Purchase #2	$168.46	10.176%	$185.6025	$185.60	$185.60	$185.60
Purchase #3	$51.55	4.229%	$53.73	$53.73	$53.75	$53.70
Purchase #4	$72.81	7.433%	$78.222	$78.22	$78.20	$78.20
Purchase #5	$86.74	4.517%	$90.658	$90.66	$90.65	$90.70
Purchase #6	$234.62	10.766%	$259.8792	$259.88	$259.90	$259.90
Purchase #7	$48.64	8.755%	$52.8984	$52.90	$52.90	$52.90
7 purchase totals =	$740.58		$804.6101	$804.61	$804.60	$804.60