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	$112.54	13.103%	$127.2861	$127.29	$127.30	$127.30
Purchase #2	$174.50	12.845%	$196.9145	$196.91	$196.90	$196.90
Purchase #3	$16.38	7.637%	$17.6309	$17.63	$17.65	$17.60
Purchase #4	$115.98	13.486%	$131.6211	$131.62	$131.60	$131.60
Purchase #5	$183.84	8.637%	$199.7183	$199.72	$199.70	$199.70
Purchase #6	$82.59	3.444%	$85.4344	$85.43	$85.45	$85.40
Purchase #7	$150.73	7.753%	$162.4161	$162.42	$162.40	$162.40
7 purchase totals =	$836.56		$921.0214	$921.02	$921.00	$920.90