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	$102.47	8.398%	$111.0754	$111.08	$111.10	$111.10
Purchase #2	$210.79	8.840%	$229.4238	$229.42	$229.40	$229.40
Purchase #3	$51.86	9.613%	$56.8453	$56.85	$56.85	$56.80
Purchase #4	$135.26	3.132%	$139.4963	$139.50	$139.50	$139.50
Purchase #5	$179.93	8.707%	$195.5965	$195.60	$195.60	$195.60
Purchase #6	$246.28	3.851%	$255.7642	$255.76	$255.75	$255.80
Purchase #7	$239.47	12.183%	$268.6446	$268.64	$268.65	$268.60
7 purchase totals =	$1,166.06		$1,256.8461	$1,256.85	$1,256.85	$1,256.80