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	$135.27	7.392%	$145.2692	$145.27	$145.25	$145.30
Purchase #2	$111.63	10.673%	$123.5443	$123.54	$123.55	$123.50
Purchase #3	$31.59	8.610%	$34.3099	$34.31	$34.30	$34.30
Purchase #4	$47.40	8.318%	$51.3427	$51.34	$51.35	$51.30
Purchase #5	$141.95	8.631%	$154.2017	$154.20	$154.20	$154.20
Purchase #6	$41.92	8.830%	$45.6215	$45.62	$45.60	$45.60
Purchase #7	$110.51	3.250%	$114.1016	$114.10	$114.10	$114.10
7 purchase totals =	$620.27		$668.3909	$668.38	$668.35	$668.30