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	$9.94	6.831%	$10.619	$10.62	$10.60	$10.60
Purchase #2	$149.74	11.678%	$167.2266	$167.23	$167.25	$167.20
Purchase #3	$204.48	3.866%	$212.3852	$212.39	$212.40	$212.40
Purchase #4	$168.98	5.854%	$178.8721	$178.87	$178.85	$178.90
Purchase #5	$173.69	5.121%	$182.5847	$182.58	$182.60	$182.60
Purchase #6	$43.52	4.441%	$45.4527	$45.45	$45.45	$45.50
Purchase #7	$133.39	6.243%	$141.7175	$141.72	$141.70	$141.70
7 purchase totals =	$883.74		$938.8578	$938.86	$938.85	$938.90