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	$52.43	8.506%	$56.8897	$56.89	$56.90	$56.90
Purchase #2	$60.55	8.193%	$65.5109	$65.51	$65.50	$65.50
Purchase #3	$160.99	7.251%	$172.6634	$172.66	$172.65	$172.70
Purchase #4	$101.46	4.861%	$106.392	$106.39	$106.40	$106.40
Purchase #5	$112.45	12.442%	$126.441	$126.44	$126.45	$126.40
Purchase #6	$115.43	10.488%	$127.5363	$127.54	$127.55	$127.50
Purchase #7	$148.85	7.302%	$159.719	$159.72	$159.70	$159.70
7 purchase totals =	$752.16		$815.1523	$815.15	$815.15	$815.10