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	$105.36	12.845%	$118.8935	$118.89	$118.90	$118.90
Purchase #2	$49.81	3.657%	$51.6316	$51.63	$51.65	$51.60
Purchase #3	$244.31	3.596%	$253.0954	$253.10	$253.10	$253.10
Purchase #4	$157.29	5.813%	$166.4333	$166.43	$166.45	$166.40
Purchase #5	$228.73	5.742%	$241.8637	$241.86	$241.85	$241.90
Purchase #6	$89.30	11.642%	$99.6963	$99.70	$99.70	$99.70
Purchase #7	$239.33	7.292%	$256.7819	$256.78	$256.80	$256.80
7 purchase totals =	$1,114.13		$1,188.3957	$1,188.39	$1,188.45	$1,188.40