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	$28.33	3.403%	$29.2941	$29.29	$29.30	$29.30
Purchase #2	$168.94	5.580%	$178.3669	$178.37	$178.35	$178.40
Purchase #3	$249.28	10.837%	$276.2945	$276.29	$276.30	$276.30
Purchase #4	$147.85	13.211%	$167.3825	$167.38	$167.40	$167.40
Purchase #5	$96.32	13.708%	$109.5235	$109.52	$109.50	$109.50
Purchase #6	$217.38	11.250%	$241.8353	$241.84	$241.85	$241.80
Purchase #7	$238.86	3.763%	$247.8483	$247.85	$247.85	$247.80
7 purchase totals =	$1,146.96		$1,250.5451	$1,250.54	$1,250.55	$1,250.50