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	$45.86	8.206%	$49.6233	$49.62	$49.60	$49.60
Purchase #2	$131.94	9.788%	$144.8543	$144.85	$144.85	$144.90
Purchase #3	$165.44	3.564%	$171.3363	$171.34	$171.35	$171.30
Purchase #4	$115.34	3.834%	$119.7621	$119.76	$119.75	$119.80
Purchase #5	$171.64	5.844%	$181.6706	$181.67	$181.65	$181.70
Purchase #6	$151.66	9.559%	$166.1572	$166.16	$166.15	$166.20
Purchase #7	$83.63	7.669%	$90.0436	$90.04	$90.05	$90.00
7 purchase totals =	$865.51		$923.4474	$923.44	$923.40	$923.50