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	$134.65	13.529%	$152.8668	$152.87	$152.85	$152.90
Purchase #2	$190.68	4.315%	$198.9078	$198.91	$198.90	$198.90
Purchase #3	$89.28	11.491%	$99.5392	$99.54	$99.55	$99.50
Purchase #4	$228.44	12.205%	$256.3211	$256.32	$256.30	$256.30
Purchase #5	$134.44	5.411%	$141.7145	$141.71	$141.70	$141.70
Purchase #6	$132.87	9.662%	$145.7079	$145.71	$145.70	$145.70
Purchase #7	$101.31	13.112%	$114.5938	$114.59	$114.60	$114.60
7 purchase totals =	$1,011.67		$1,109.6511	$1,109.65	$1,109.60	$1,109.60