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	$78.88	5.621%	$83.3138	$83.31	$83.30	$83.30
Purchase #2	$116.63	11.105%	$129.5818	$129.58	$129.60	$129.60
Purchase #3	$66.33	10.296%	$73.1593	$73.16	$73.15	$73.20
Purchase #4	$173.63	7.280%	$186.2703	$186.27	$186.25	$186.30
Purchase #5	$175.65	5.646%	$185.5672	$185.57	$185.55	$185.60
Purchase #6	$96.51	3.219%	$99.6167	$99.62	$99.60	$99.60
Purchase #7	$59.42	9.827%	$65.2592	$65.26	$65.25	$65.30
7 purchase totals =	$767.05		$822.7683	$822.77	$822.70	$822.90