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	$123.84	11.231%	$137.7485	$137.75	$137.75	$137.70
Purchase #2	$62.61	6.362%	$66.5932	$66.59	$66.60	$66.60
Purchase #3	$150.61	9.659%	$165.1574	$165.16	$165.15	$165.20
Purchase #4	$65.34	12.236%	$73.335	$73.34	$73.35	$73.30
Purchase #5	$149.85	11.735%	$167.4349	$167.43	$167.45	$167.40
Purchase #6	$234.48	8.576%	$254.589	$254.59	$254.60	$254.60
Purchase #7	$68.31	5.746%	$72.2351	$72.24	$72.25	$72.20
7 purchase totals =	$855.04		$937.0931	$937.10	$937.15	$937.00