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	$178.29	9.688%	$195.5627	$195.56	$195.55	$195.60
Purchase #2	$121.90	4.198%	$127.0174	$127.02	$127.00	$127.00
Purchase #3	$167.92	9.581%	$184.0084	$184.01	$184.00	$184.00
Purchase #4	$91.79	13.671%	$104.3386	$104.34	$104.35	$104.30
Purchase #5	$34.82	7.486%	$37.4266	$37.43	$37.45	$37.40
Purchase #6	$152.59	11.722%	$170.4766	$170.48	$170.50	$170.50
Purchase #7	$170.30	6.125%	$180.7309	$180.73	$180.75	$180.70
7 purchase totals =	$917.61		$999.5612	$999.57	$999.60	$999.50