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	$48.76	13.638%	$55.4099	$55.41	$55.40	$55.40
Purchase #2	$82.98	7.733%	$89.3968	$89.40	$89.40	$89.40
Purchase #3	$135.95	6.618%	$144.9472	$144.95	$144.95	$144.90
Purchase #4	$62.75	9.312%	$68.5933	$68.59	$68.60	$68.60
Purchase #5	$115.30	7.837%	$124.3361	$124.34	$124.35	$124.30
Purchase #6	$85.61	5.693%	$90.4838	$90.48	$90.50	$90.50
Purchase #7	$113.83	8.871%	$123.9279	$123.93	$123.95	$123.90
7 purchase totals =	$645.18		$697.0950	$697.10	$697.15	$697.00