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	$100.32	12.414%	$112.7737	$112.77	$112.75	$112.80
Purchase #2	$26.60	4.278%	$27.7379	$27.74	$27.75	$27.70
Purchase #3	$204.94	12.348%	$230.246	$230.25	$230.25	$230.20
Purchase #4	$81.78	9.567%	$89.6039	$89.60	$89.60	$89.60
Purchase #5	$150.50	3.226%	$155.3551	$155.36	$155.35	$155.40
Purchase #6	$80.25	12.766%	$90.4947	$90.49	$90.50	$90.50
Purchase #7	$121.34	12.510%	$136.5196	$136.52	$136.50	$136.50
7 purchase totals =	$765.73		$842.7309	$842.73	$842.70	$842.70