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	$161.31	11.279%	$179.5042	$179.50	$179.50	$179.50
Purchase #2	$108.78	5.658%	$114.9348	$114.93	$114.95	$114.90
Purchase #3	$33.74	4.518%	$35.2644	$35.26	$35.25	$35.30
Purchase #4	$57.38	7.825%	$61.87	$61.87	$61.85	$61.90
Purchase #5	$36.69	10.467%	$40.5303	$40.53	$40.55	$40.50
Purchase #6	$181.62	5.675%	$191.9269	$191.93	$191.95	$191.90
Purchase #7	$59.29	5.603%	$62.612	$62.61	$62.60	$62.60
7 purchase totals =	$638.81		$686.6426	$686.63	$686.65	$686.60