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	$136.92	12.122%	$153.5174	$153.52	$153.50	$153.50
Purchase #2	$216.86	12.295%	$243.5229	$243.52	$243.50	$243.50
Purchase #3	$217.94	13.399%	$247.1418	$247.14	$247.15	$247.10
Purchase #4	$65.52	13.451%	$74.3331	$74.33	$74.35	$74.30
Purchase #5	$93.97	7.725%	$101.2292	$101.23	$101.25	$101.20
Purchase #6	$85.52	5.153%	$89.9268	$89.93	$89.95	$89.90
Purchase #7	$112.79	6.741%	$120.3932	$120.39	$120.40	$120.40
7 purchase totals =	$929.52		$1,030.0644	$1,030.06	$1,030.10	$1,029.90