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	$177.63	4.223%	$185.1313	$185.13	$185.15	$185.10
Purchase #2	$83.30	7.350%	$89.4226	$89.42	$89.40	$89.40
Purchase #3	$172.42	8.251%	$186.6464	$186.65	$186.65	$186.60
Purchase #4	$245.51	7.218%	$263.2309	$263.23	$263.25	$263.20
Purchase #5	$84.72	11.655%	$94.5941	$94.59	$94.60	$94.60
Purchase #6	$23.26	10.421%	$25.6839	$25.68	$25.70	$25.70
Purchase #7	$127.53	13.648%	$144.9353	$144.94	$144.95	$144.90
7 purchase totals =	$914.37		$989.6445	$989.64	$989.70	$989.50