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	$99.78	3.145%	$102.9181	$102.92	$102.90	$102.90
Purchase #2	$158.92	4.166%	$165.5406	$165.54	$165.55	$165.50
Purchase #3	$145.86	6.846%	$155.8456	$155.85	$155.85	$155.80
Purchase #4	$229.58	5.296%	$241.7386	$241.74	$241.75	$241.70
Purchase #5	$170.44	12.380%	$191.5405	$191.54	$191.55	$191.50
Purchase #6	$152.50	4.167%	$158.8547	$158.85	$158.85	$158.90
Purchase #7	$161.35	6.716%	$172.1863	$172.19	$172.20	$172.20
7 purchase totals =	$1,118.43		$1,188.6244	$1,188.63	$1,188.65	$1,188.50