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	$141.97	10.756%	$157.2403	$157.24	$157.25	$157.20
Purchase #2	$96.25	3.692%	$99.8036	$99.80	$99.80	$99.80
Purchase #3	$112.76	12.701%	$127.0816	$127.08	$127.10	$127.10
Purchase #4	$52.99	12.369%	$59.5443	$59.54	$59.55	$59.50
Purchase #5	$172.41	9.757%	$189.232	$189.23	$189.25	$189.20
Purchase #6	$20.45	11.377%	$22.7766	$22.78	$22.80	$22.80
Purchase #7	$181.63	5.187%	$191.0511	$191.05	$191.05	$191.10
7 purchase totals =	$778.46		$846.7295	$846.72	$846.80	$846.70