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	$44.88	12.680%	$50.5708	$50.57	$50.55	$50.60
Purchase #2	$168.38	3.360%	$174.0376	$174.04	$174.05	$174.00
Purchase #3	$93.30	7.831%	$100.6063	$100.61	$100.60	$100.60
Purchase #4	$63.59	11.528%	$70.9207	$70.92	$70.90	$70.90
Purchase #5	$29.82	7.685%	$32.1117	$32.11	$32.10	$32.10
Purchase #6	$122.89	9.258%	$134.2672	$134.27	$134.25	$134.30
Purchase #7	$181.52	13.139%	$205.3699	$205.37	$205.35	$205.40
7 purchase totals =	$704.38		$767.8842	$767.89	$767.80	$767.90