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	$125.39	3.314%	$129.5454	$129.55	$129.55	$129.50
Purchase #2	$84.59	5.850%	$89.5385	$89.54	$89.55	$89.50
Purchase #3	$61.89	4.267%	$64.5308	$64.53	$64.55	$64.50
Purchase #4	$49.88	5.195%	$52.4713	$52.47	$52.45	$52.50
Purchase #5	$102.39	13.172%	$115.8768	$115.88	$115.90	$115.90
Purchase #6	$192.30	7.732%	$207.1686	$207.17	$207.15	$207.20
Purchase #7	$76.26	9.424%	$83.4467	$83.45	$83.45	$83.40
7 purchase totals =	$692.70		$742.5781	$742.59	$742.60	$742.50