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	$138.41	10.116%	$152.4116	$152.41	$152.40	$152.40
Purchase #2	$36.77	3.710%	$38.1342	$38.13	$38.15	$38.10
Purchase #3	$135.63	6.452%	$144.3808	$144.38	$144.40	$144.40
Purchase #4	$249.55	13.174%	$282.4257	$282.43	$282.45	$282.40
Purchase #5	$53.31	8.600%	$57.8947	$57.89	$57.90	$57.90
Purchase #6	$69.90	8.142%	$75.5913	$75.59	$75.60	$75.60
Purchase #7	$165.25	12.179%	$185.3758	$185.38	$185.40	$185.40
7 purchase totals =	$848.82		$936.2141	$936.21	$936.30	$936.20