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	$38.61	7.312%	$41.4332	$41.43	$41.45	$41.40
Purchase #2	$24.53	13.765%	$27.9066	$27.91	$27.90	$27.90
Purchase #3	$203.75	7.593%	$219.2207	$219.22	$219.20	$219.20
Purchase #4	$134.70	3.655%	$139.6233	$139.62	$139.60	$139.60
Purchase #5	$88.30	10.731%	$97.7755	$97.78	$97.80	$97.80
Purchase #6	$77.29	11.361%	$86.0709	$86.07	$86.05	$86.10
Purchase #7	$40.64	4.408%	$42.4314	$42.43	$42.45	$42.40
7 purchase totals =	$607.82		$654.4616	$654.46	$654.45	$654.40