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	$166.39	12.424%	$187.0623	$187.06	$187.05	$187.10
Purchase #2	$142.73	13.766%	$162.3782	$162.38	$162.40	$162.40
Purchase #3	$143.86	10.869%	$159.4961	$159.50	$159.50	$159.50
Purchase #4	$59.81	4.410%	$62.4476	$62.45	$62.45	$62.40
Purchase #5	$158.70	9.270%	$173.4115	$173.41	$173.40	$173.40
Purchase #6	$170.34	10.683%	$188.5374	$188.54	$188.55	$188.50
Purchase #7	$31.87	7.605%	$34.2937	$34.29	$34.30	$34.30
7 purchase totals =	$873.70		$967.6268	$967.63	$967.65	$967.60