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	$84.95	6.319%	$90.318	$90.32	$90.30	$90.30
Purchase #2	$145.36	7.301%	$155.9727	$155.97	$155.95	$156.00
Purchase #3	$54.27	12.584%	$61.0993	$61.10	$61.10	$61.10
Purchase #4	$38.93	10.612%	$43.0613	$43.06	$43.05	$43.10
Purchase #5	$40.96	5.188%	$43.085	$43.09	$43.10	$43.10
Purchase #6	$69.29	8.405%	$75.1138	$75.11	$75.10	$75.10
Purchase #7	$226.72	13.195%	$256.6357	$256.64	$256.65	$256.60
7 purchase totals =	$660.48		$725.2858	$725.29	$725.25	$725.30