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	$129.98	3.840%	$134.9712	$134.97	$134.95	$135.00
Purchase #2	$230.88	10.605%	$255.3648	$255.36	$255.35	$255.40
Purchase #3	$162.62	6.840%	$173.7432	$173.74	$173.75	$173.70
Purchase #4	$99.36	12.225%	$111.5068	$111.51	$111.50	$111.50
Purchase #5	$164.34	12.285%	$184.5292	$184.53	$184.55	$184.50
Purchase #6	$174.79	7.631%	$188.1282	$188.13	$188.15	$188.10
Purchase #7	$112.76	5.224%	$118.6506	$118.65	$118.65	$118.70
7 purchase totals =	$1,074.73		$1,166.8940	$1,166.89	$1,166.90	$1,166.90