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	$56.42	13.308%	$63.9284	$63.93	$63.95	$63.90
Purchase #2	$90.98	8.408%	$98.6296	$98.63	$98.65	$98.60
Purchase #3	$223.64	6.182%	$237.4654	$237.47	$237.45	$237.50
Purchase #4	$103.60	11.532%	$115.5472	$115.55	$115.55	$115.50
Purchase #5	$72.84	10.567%	$80.537	$80.54	$80.55	$80.50
Purchase #6	$65.66	9.615%	$71.9732	$71.97	$71.95	$72.00
Purchase #7	$39.68	9.658%	$43.5123	$43.51	$43.50	$43.50
7 purchase totals =	$652.82		$711.5931	$711.60	$711.60	$711.50