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	$178.94	13.577%	$203.2347	$203.23	$203.25	$203.20
Purchase #2	$120.65	12.853%	$136.1571	$136.16	$136.15	$136.20
Purchase #3	$181.32	3.531%	$187.7224	$187.72	$187.70	$187.70
Purchase #4	$49.65	6.789%	$53.0207	$53.02	$53.00	$53.00
Purchase #5	$98.46	4.748%	$103.1349	$103.13	$103.15	$103.10
Purchase #6	$74.55	10.369%	$82.2801	$82.28	$82.30	$82.30
Purchase #7	$43.89	10.807%	$48.6332	$48.63	$48.65	$48.60
7 purchase totals =	$747.46		$814.1831	$814.17	$814.20	$814.10