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	$109.69	6.153%	$116.4392	$116.44	$116.45	$116.40
Purchase #2	$231.71	5.439%	$244.3127	$244.31	$244.30	$244.30
Purchase #3	$193.90	10.326%	$213.9221	$213.92	$213.90	$213.90
Purchase #4	$186.37	12.193%	$209.0941	$209.09	$209.10	$209.10
Purchase #5	$107.58	3.803%	$111.6713	$111.67	$111.65	$111.70
Purchase #6	$96.95	10.286%	$106.9223	$106.92	$106.90	$106.90
Purchase #7	$79.82	13.121%	$90.2932	$90.29	$90.30	$90.30
7 purchase totals =	$1,006.02		$1,092.6549	$1,092.64	$1,092.60	$1,092.60