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	$52.83	11.702%	$59.0122	$59.01	$59.00	$59.00
Purchase #2	$94.37	10.617%	$104.3893	$104.39	$104.40	$104.40
Purchase #3	$97.72	7.247%	$104.8018	$104.80	$104.80	$104.80
Purchase #4	$216.91	10.503%	$239.6921	$239.69	$239.70	$239.70
Purchase #5	$74.77	6.218%	$79.4192	$79.42	$79.40	$79.40
Purchase #6	$151.88	13.580%	$172.5053	$172.51	$172.50	$172.50
Purchase #7	$109.73	7.331%	$117.7743	$117.77	$117.75	$117.80
7 purchase totals =	$798.21		$877.5942	$877.59	$877.55	$877.60