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	$27.41	5.726%	$28.9795	$28.98	$29.00	$29.00
Purchase #2	$62.43	9.413%	$68.3065	$68.31	$68.30	$68.30
Purchase #3	$156.35	9.110%	$170.5935	$170.59	$170.60	$170.60
Purchase #4	$137.89	6.264%	$146.5274	$146.53	$146.55	$146.50
Purchase #5	$51.25	9.825%	$56.2853	$56.29	$56.30	$56.30
Purchase #6	$97.55	8.520%	$105.8613	$105.86	$105.85	$105.90
Purchase #7	$145.46	13.329%	$164.8484	$164.85	$164.85	$164.80
7 purchase totals =	$678.34		$741.4019	$741.41	$741.45	$741.40