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	$241.99	5.689%	$255.7568	$255.76	$255.75	$255.80
Purchase #2	$228.54	8.830%	$248.7201	$248.72	$248.70	$248.70
Purchase #3	$160.26	7.806%	$172.7699	$172.77	$172.75	$172.80
Purchase #4	$54.28	9.786%	$59.5918	$59.59	$59.60	$59.60
Purchase #5	$148.71	7.626%	$160.0506	$160.05	$160.05	$160.10
Purchase #6	$58.92	6.203%	$62.5748	$62.57	$62.55	$62.60
Purchase #7	$249.96	9.573%	$273.8887	$273.89	$273.90	$273.90
7 purchase totals =	$1,142.66		$1,233.3527	$1,233.35	$1,233.30	$1,233.50