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	$26.81	3.445%	$27.7336	$27.73	$27.75	$27.70
Purchase #2	$141.94	9.662%	$155.6542	$155.65	$155.65	$155.70
Purchase #3	$72.70	8.182%	$78.6483	$78.65	$78.65	$78.60
Purchase #4	$137.96	5.255%	$145.2098	$145.21	$145.20	$145.20
Purchase #5	$243.68	12.749%	$274.7468	$274.75	$274.75	$274.70
Purchase #6	$33.84	10.211%	$37.2954	$37.30	$37.30	$37.30
Purchase #7	$74.90	4.581%	$78.3312	$78.33	$78.35	$78.30
7 purchase totals =	$731.83		$797.6193	$797.62	$797.65	$797.50