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	$36.95	7.480%	$39.7139	$39.71	$39.70	$39.70
Purchase #2	$36.60	3.243%	$37.7869	$37.79	$37.80	$37.80
Purchase #3	$89.91	7.802%	$96.9248	$96.92	$96.90	$96.90
Purchase #4	$100.85	7.737%	$108.6528	$108.65	$108.65	$108.70
Purchase #5	$123.28	6.432%	$131.2094	$131.21	$131.20	$131.20
Purchase #6	$168.66	3.719%	$174.9325	$174.93	$174.95	$174.90
Purchase #7	$139.65	13.314%	$158.243	$158.24	$158.25	$158.20
7 purchase totals =	$695.90		$747.4633	$747.45	$747.45	$747.40