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	$155.56	12.190%	$174.5228	$174.52	$174.50	$174.50
Purchase #2	$10.40	4.520%	$10.8701	$10.87	$10.85	$10.90
Purchase #3	$150.73	10.279%	$166.2235	$166.22	$166.20	$166.20
Purchase #4	$188.82	4.114%	$196.5881	$196.59	$196.60	$196.60
Purchase #5	$38.54	11.218%	$42.8634	$42.86	$42.85	$42.90
Purchase #6	$228.59	13.125%	$258.5924	$258.59	$258.60	$258.60
Purchase #7	$205.90	11.225%	$229.0123	$229.01	$229.00	$229.00
7 purchase totals =	$978.54		$1,078.6726	$1,078.66	$1,078.60	$1,078.70