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	$110.81	3.676%	$114.8834	$114.88	$114.90	$114.90
Purchase #2	$136.63	13.556%	$155.1516	$155.15	$155.15	$155.20
Purchase #3	$50.44	4.857%	$52.8899	$52.89	$52.90	$52.90
Purchase #4	$14.54	9.503%	$15.9217	$15.92	$15.90	$15.90
Purchase #5	$109.89	10.219%	$121.1197	$121.12	$121.10	$121.10
Purchase #6	$152.48	13.187%	$172.5875	$172.59	$172.60	$172.60
Purchase #7	$75.29	7.370%	$80.8389	$80.84	$80.85	$80.80
7 purchase totals =	$650.08		$713.3927	$713.39	$713.40	$713.40