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	$93.84	3.135%	$96.7819	$96.78	$96.80	$96.80
Purchase #2	$53.78	10.174%	$59.2516	$59.25	$59.25	$59.30
Purchase #3	$80.55	13.475%	$91.4041	$91.40	$91.40	$91.40
Purchase #4	$27.72	5.793%	$29.3258	$29.33	$29.35	$29.30
Purchase #5	$55.38	3.684%	$57.4202	$57.42	$57.40	$57.40
Purchase #6	$24.95	10.694%	$27.6182	$27.62	$27.60	$27.60
Purchase #7	$161.52	10.467%	$178.4263	$178.43	$178.45	$178.40
7 purchase totals =	$497.74		$540.2281	$540.23	$540.25	$540.20