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	$55.30	4.168%	$57.6049	$57.60	$57.60	$57.60
Purchase #2	$57.33	4.366%	$59.833	$59.83	$59.85	$59.80
Purchase #3	$135.28	11.543%	$150.8954	$150.90	$150.90	$150.90
Purchase #4	$148.27	13.626%	$168.4733	$168.47	$168.45	$168.50
Purchase #5	$36.33	11.386%	$40.4665	$40.47	$40.45	$40.50
Purchase #6	$188.93	8.322%	$204.6528	$204.65	$204.65	$204.70
Purchase #7	$113.38	5.161%	$119.2315	$119.23	$119.25	$119.20
7 purchase totals =	$734.82		$801.1574	$801.15	$801.15	$801.20