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	$113.38	13.209%	$128.3564	$128.36	$128.35	$128.40
Purchase #2	$153.67	13.337%	$174.165	$174.17	$174.15	$174.20
Purchase #3	$111.37	10.764%	$123.3579	$123.36	$123.35	$123.40
Purchase #4	$186.94	12.158%	$209.6682	$209.67	$209.65	$209.70
Purchase #5	$165.47	8.864%	$180.1373	$180.14	$180.15	$180.10
Purchase #6	$61.49	7.774%	$66.2702	$66.27	$66.25	$66.30
Purchase #7	$137.82	11.698%	$153.9422	$153.94	$153.95	$153.90
7 purchase totals =	$930.14		$1,035.8972	$1,035.91	$1,035.85	$1,036.00