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	$17.51	13.366%	$19.8504	$19.85	$19.85	$19.90
Purchase #2	$18.36	9.199%	$20.0489	$20.05	$20.05	$20.00
Purchase #3	$238.54	7.732%	$256.9839	$256.98	$257.00	$257.00
Purchase #4	$132.53	12.819%	$149.519	$149.52	$149.50	$149.50
Purchase #5	$78.50	5.350%	$82.6998	$82.70	$82.70	$82.70
Purchase #6	$42.61	7.560%	$45.8313	$45.83	$45.85	$45.80
Purchase #7	$50.61	7.557%	$54.4346	$54.43	$54.45	$54.40
7 purchase totals =	$578.66		$629.3679	$629.36	$629.40	$629.30