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	$51.29	10.245%	$56.5447	$56.54	$56.55	$56.50
Purchase #2	$139.54	4.829%	$146.2784	$146.28	$146.30	$146.30
Purchase #3	$119.77	4.448%	$125.0974	$125.10	$125.10	$125.10
Purchase #4	$136.34	7.848%	$147.04	$147.04	$147.05	$147.00
Purchase #5	$189.78	4.616%	$198.5402	$198.54	$198.55	$198.50
Purchase #6	$89.75	13.670%	$102.0188	$102.02	$102.00	$102.00
Purchase #7	$41.34	3.340%	$42.7208	$42.72	$42.70	$42.70
7 purchase totals =	$767.81		$818.2403	$818.24	$818.25	$818.10