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	$10.25	11.384%	$11.4169	$11.42	$11.40	$11.40
Purchase #2	$139.55	3.476%	$144.4008	$144.40	$144.40	$144.40
Purchase #3	$28.87	4.626%	$30.2055	$30.21	$30.20	$30.20
Purchase #4	$53.50	4.420%	$55.8647	$55.86	$55.85	$55.90
Purchase #5	$114.61	3.233%	$118.3153	$118.32	$118.30	$118.30
Purchase #6	$6.42	9.287%	$7.0162	$7.02	$7.00	$7.00
Purchase #7	$73.86	5.835%	$78.1697	$78.17	$78.15	$78.20
7 purchase totals =	$427.06		$445.3891	$445.40	$445.30	$445.40