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	$173.33	3.189%	$178.8575	$178.86	$178.85	$178.90
Purchase #2	$90.76	10.135%	$99.9585	$99.96	$99.95	$100.00
Purchase #3	$152.79	8.222%	$165.3524	$165.35	$165.35	$165.40
Purchase #4	$137.75	13.483%	$156.3228	$156.32	$156.30	$156.30
Purchase #5	$238.56	11.682%	$266.4286	$266.43	$266.45	$266.40
Purchase #6	$127.92	13.804%	$145.5781	$145.58	$145.60	$145.60
Purchase #7	$229.48	7.307%	$246.2481	$246.25	$246.25	$246.20
7 purchase totals =	$1,150.59		$1,258.7460	$1,258.75	$1,258.75	$1,258.80