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	$141.80	9.871%	$155.7971	$155.80	$155.80	$155.80
Purchase #2	$54.39	5.209%	$57.2232	$57.22	$57.20	$57.20
Purchase #3	$147.94	10.871%	$164.0226	$164.02	$164.00	$164.00
Purchase #4	$99.81	10.333%	$110.1234	$110.12	$110.10	$110.10
Purchase #5	$90.28	11.257%	$100.4428	$100.44	$100.45	$100.40
Purchase #6	$180.61	7.629%	$194.3887	$194.39	$194.40	$194.40
Purchase #7	$67.46	10.853%	$74.7814	$74.78	$74.80	$74.80
7 purchase totals =	$782.29		$856.7792	$856.77	$856.75	$856.70