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	$183.69	13.399%	$208.3026	$208.30	$208.30	$208.30
Purchase #2	$158.91	8.856%	$172.9831	$172.98	$173.00	$173.00
Purchase #3	$165.91	8.365%	$179.7884	$179.79	$179.80	$179.80
Purchase #4	$237.89	8.535%	$258.1939	$258.19	$258.20	$258.20
Purchase #5	$203.64	10.397%	$224.8125	$224.81	$224.80	$224.80
Purchase #6	$188.59	6.360%	$200.5843	$200.58	$200.60	$200.60
Purchase #7	$80.68	12.192%	$90.5165	$90.52	$90.50	$90.50
7 purchase totals =	$1,219.31		$1,335.1813	$1,335.17	$1,335.20	$1,335.20