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	$145.83	7.164%	$156.2773	$156.28	$156.30	$156.30
Purchase #2	$190.72	9.518%	$208.8727	$208.87	$208.85	$208.90
Purchase #3	$237.26	13.135%	$268.4241	$268.42	$268.40	$268.40
Purchase #4	$60.29	5.486%	$63.5975	$63.60	$63.60	$63.60
Purchase #5	$115.90	13.218%	$131.2197	$131.22	$131.20	$131.20
Purchase #6	$209.88	6.687%	$223.9147	$223.91	$223.90	$223.90
Purchase #7	$17.73	3.859%	$18.4142	$18.41	$18.40	$18.40
7 purchase totals =	$977.61		$1,070.7202	$1,070.71	$1,070.65	$1,070.70