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	$82.65	8.439%	$89.6248	$89.62	$89.60	$89.60
Purchase #2	$141.69	12.133%	$158.8812	$158.88	$158.90	$158.90
Purchase #3	$188.44	10.337%	$207.919	$207.92	$207.90	$207.90
Purchase #4	$182.95	12.599%	$205.9999	$206.00	$206.00	$206.00
Purchase #5	$214.52	3.565%	$222.1676	$222.17	$222.15	$222.20
Purchase #6	$185.64	11.155%	$206.3481	$206.35	$206.35	$206.30
Purchase #7	$165.59	5.444%	$174.6047	$174.60	$174.60	$174.60
7 purchase totals =	$1,161.48		$1,265.5453	$1,265.54	$1,265.50	$1,265.50