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	$137.26	12.544%	$154.4779	$154.48	$154.50	$154.50
Purchase #2	$181.94	4.280%	$189.727	$189.73	$189.75	$189.70
Purchase #3	$46.98	13.596%	$53.3674	$53.37	$53.35	$53.40
Purchase #4	$99.95	3.670%	$103.6182	$103.62	$103.60	$103.60
Purchase #5	$238.46	11.594%	$266.1071	$266.11	$266.10	$266.10
Purchase #6	$159.63	10.636%	$176.6082	$176.61	$176.60	$176.60
Purchase #7	$121.33	13.335%	$137.5094	$137.51	$137.50	$137.50
7 purchase totals =	$985.55		$1,081.4152	$1,081.43	$1,081.40	$1,081.40