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	$189.58	11.509%	$211.3988	$211.40	$211.40	$211.40
Purchase #2	$146.81	8.190%	$158.8337	$158.83	$158.85	$158.80
Purchase #3	$111.89	11.674%	$124.952	$124.95	$124.95	$125.00
Purchase #4	$94.72	11.256%	$105.3817	$105.38	$105.40	$105.40
Purchase #5	$62.85	7.755%	$67.724	$67.72	$67.70	$67.70
Purchase #6	$101.74	11.707%	$113.6507	$113.65	$113.65	$113.70
Purchase #7	$37.69	13.679%	$42.8456	$42.85	$42.85	$42.80
7 purchase totals =	$745.28		$824.7865	$824.78	$824.80	$824.80