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	$160.29	4.131%	$166.9116	$166.91	$166.90	$166.90
Purchase #2	$137.29	11.129%	$152.569	$152.57	$152.55	$152.60
Purchase #3	$184.61	12.726%	$208.1035	$208.10	$208.10	$208.10
Purchase #4	$167.93	7.531%	$180.5768	$180.58	$180.60	$180.60
Purchase #5	$132.41	3.648%	$137.2403	$137.24	$137.25	$137.20
Purchase #6	$127.67	10.231%	$140.7319	$140.73	$140.75	$140.70
Purchase #7	$224.39	13.594%	$254.8936	$254.89	$254.90	$254.90
7 purchase totals =	$1,134.59		$1,241.0267	$1,241.02	$1,241.05	$1,241.00