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	$136.42	10.330%	$150.5122	$150.51	$150.50	$150.50
Purchase #2	$36.42	7.476%	$39.1428	$39.14	$39.15	$39.10
Purchase #3	$34.82	12.531%	$39.1833	$39.18	$39.20	$39.20
Purchase #4	$126.80	11.498%	$141.3795	$141.38	$141.40	$141.40
Purchase #5	$135.92	5.445%	$143.3208	$143.32	$143.30	$143.30
Purchase #6	$179.85	6.535%	$191.6032	$191.60	$191.60	$191.60
Purchase #7	$156.60	10.307%	$172.7408	$172.74	$172.75	$172.70
7 purchase totals =	$806.83		$877.8826	$877.87	$877.90	$877.80