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	$90.25	10.361%	$99.6008	$99.60	$99.60	$99.60
Purchase #2	$240.50	4.195%	$250.589	$250.59	$250.60	$250.60
Purchase #3	$19.94	13.412%	$22.6144	$22.61	$22.60	$22.60
Purchase #4	$118.86	6.200%	$126.2293	$126.23	$126.25	$126.20
Purchase #5	$182.82	8.225%	$197.8569	$197.86	$197.85	$197.90
Purchase #6	$235.39	13.828%	$267.9397	$267.94	$267.95	$267.90
Purchase #7	$212.85	10.520%	$235.2418	$235.24	$235.25	$235.20
7 purchase totals =	$1,100.61		$1,200.0719	$1,200.07	$1,200.10	$1,200.00