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	$169.51	5.403%	$178.6686	$178.67	$178.65	$178.70
Purchase #2	$60.30	10.102%	$66.3915	$66.39	$66.40	$66.40
Purchase #3	$116.33	12.561%	$130.9422	$130.94	$130.95	$130.90
Purchase #4	$38.98	12.643%	$43.9082	$43.91	$43.90	$43.90
Purchase #5	$70.84	3.610%	$73.3973	$73.40	$73.40	$73.40
Purchase #6	$71.42	10.425%	$78.8655	$78.87	$78.85	$78.90
Purchase #7	$147.87	13.803%	$168.2805	$168.28	$168.30	$168.30
7 purchase totals =	$675.25		$740.4538	$740.46	$740.45	$740.50