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	$37.89	12.735%	$42.7153	$42.72	$42.70	$42.70
Purchase #2	$127.32	5.732%	$134.618	$134.62	$134.60	$134.60
Purchase #3	$24.95	9.684%	$27.3662	$27.37	$27.35	$27.40
Purchase #4	$131.73	11.544%	$146.9369	$146.94	$146.95	$146.90
Purchase #5	$146.83	13.668%	$166.8987	$166.90	$166.90	$166.90
Purchase #6	$198.64	6.420%	$211.3927	$211.39	$211.40	$211.40
Purchase #7	$28.80	5.820%	$30.4762	$30.48	$30.50	$30.50
7 purchase totals =	$696.16		$760.4040	$760.42	$760.40	$760.40