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	$100.36	13.109%	$113.5162	$113.52	$113.50	$113.50
Purchase #2	$80.95	11.332%	$90.1233	$90.12	$90.10	$90.10
Purchase #3	$122.77	6.316%	$130.5242	$130.52	$130.50	$130.50
Purchase #4	$48.30	5.229%	$50.8256	$50.83	$50.85	$50.80
Purchase #5	$115.49	11.631%	$128.9226	$128.92	$128.90	$128.90
Purchase #6	$205.39	11.172%	$228.3362	$228.34	$228.35	$228.30
Purchase #7	$176.48	12.655%	$198.8135	$198.81	$198.80	$198.80
7 purchase totals =	$849.74		$941.0616	$941.06	$941.00	$940.90