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	$18.86	3.850%	$19.5861	$19.59	$19.60	$19.60
Purchase #2	$185.69	8.131%	$200.7885	$200.79	$200.80	$200.80
Purchase #3	$152.40	11.643%	$170.1439	$170.14	$170.15	$170.10
Purchase #4	$90.82	9.419%	$99.3743	$99.37	$99.35	$99.40
Purchase #5	$241.44	13.424%	$273.8509	$273.85	$273.85	$273.90
Purchase #6	$246.33	8.367%	$266.9404	$266.94	$266.95	$266.90
Purchase #7	$127.69	11.229%	$142.0283	$142.03	$142.05	$142.00
7 purchase totals =	$1,063.23		$1,172.7124	$1,172.71	$1,172.75	$1,172.70