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	$39.99	13.625%	$45.4386	$45.44	$45.45	$45.40
Purchase #2	$135.42	11.369%	$150.8159	$150.82	$150.80	$150.80
Purchase #3	$98.75	12.466%	$111.0602	$111.06	$111.05	$111.10
Purchase #4	$243.99	5.237%	$256.7678	$256.77	$256.75	$256.80
Purchase #5	$55.33	11.143%	$61.4954	$61.50	$61.50	$61.50
Purchase #6	$238.98	8.355%	$258.9468	$258.95	$258.95	$258.90
Purchase #7	$92.45	7.724%	$99.5908	$99.59	$99.60	$99.60
7 purchase totals =	$904.91		$984.1155	$984.13	$984.10	$984.10