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	$139.94	7.487%	$150.4173	$150.42	$150.40	$150.40
Purchase #2	$172.52	4.280%	$179.9039	$179.90	$179.90	$179.90
Purchase #3	$118.28	7.813%	$127.5212	$127.52	$127.50	$127.50
Purchase #4	$199.31	10.208%	$219.6556	$219.66	$219.65	$219.70
Purchase #5	$198.98	5.770%	$210.4611	$210.46	$210.45	$210.50
Purchase #6	$169.93	3.728%	$176.265	$176.27	$176.25	$176.30
Purchase #7	$176.87	8.496%	$191.8969	$191.90	$191.90	$191.90
7 purchase totals =	$1,175.83		$1,256.1210	$1,256.13	$1,256.05	$1,256.20