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	$40.89	11.823%	$45.7244	$45.72	$45.70	$45.70
Purchase #2	$101.69	3.865%	$105.6203	$105.62	$105.60	$105.60
Purchase #3	$60.66	9.498%	$66.4215	$66.42	$66.40	$66.40
Purchase #4	$232.43	4.290%	$242.4012	$242.40	$242.40	$242.40
Purchase #5	$151.97	6.815%	$162.3268	$162.33	$162.35	$162.30
Purchase #6	$68.96	13.139%	$78.0207	$78.02	$78.00	$78.00
Purchase #7	$66.47	10.605%	$73.5191	$73.52	$73.50	$73.50
7 purchase totals =	$723.07		$774.0340	$774.03	$773.95	$773.90