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	$36.35	6.515%	$38.7182	$38.72	$38.70	$38.70
Purchase #2	$120.82	13.540%	$137.179	$137.18	$137.20	$137.20
Purchase #3	$106.46	13.431%	$120.7586	$120.76	$120.75	$120.80
Purchase #4	$189.92	3.333%	$196.25	$196.25	$196.25	$196.30
Purchase #5	$105.53	4.240%	$110.0045	$110.00	$110.00	$110.00
Purchase #6	$47.87	10.448%	$52.8715	$52.87	$52.85	$52.90
Purchase #7	$136.93	7.382%	$147.0382	$147.04	$147.05	$147.00
7 purchase totals =	$743.88		$802.8200	$802.82	$802.80	$802.90