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	$170.61	5.426%	$179.8673	$179.87	$179.85	$179.90
Purchase #2	$97.92	13.690%	$111.3252	$111.33	$111.35	$111.30
Purchase #3	$125.27	13.631%	$142.3456	$142.35	$142.35	$142.30
Purchase #4	$84.92	10.533%	$93.8646	$93.86	$93.85	$93.90
Purchase #5	$62.50	5.747%	$66.0919	$66.09	$66.10	$66.10
Purchase #6	$159.26	12.185%	$178.6658	$178.67	$178.65	$178.70
Purchase #7	$66.85	6.596%	$71.2594	$71.26	$71.25	$71.30
7 purchase totals =	$767.33		$843.4198	$843.43	$843.40	$843.50