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	$97.84	7.345%	$105.0263	$105.03	$105.05	$105.00
Purchase #2	$47.53	10.301%	$52.4261	$52.43	$52.45	$52.40
Purchase #3	$96.36	13.180%	$109.0602	$109.06	$109.05	$109.10
Purchase #4	$217.71	10.752%	$241.1182	$241.12	$241.10	$241.10
Purchase #5	$140.29	12.672%	$158.0675	$158.07	$158.05	$158.10
Purchase #6	$245.76	10.586%	$271.7762	$271.78	$271.80	$271.80
Purchase #7	$55.52	3.241%	$57.3194	$57.32	$57.30	$57.30
7 purchase totals =	$901.01		$994.7939	$994.81	$994.80	$994.80