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	$80.49	13.735%	$91.5453	$91.55	$91.55	$91.50
Purchase #2	$239.92	9.527%	$262.7772	$262.78	$262.80	$262.80
Purchase #3	$215.87	12.240%	$242.2925	$242.29	$242.30	$242.30
Purchase #4	$214.81	9.738%	$235.7282	$235.73	$235.75	$235.70
Purchase #5	$143.82	5.850%	$152.2335	$152.23	$152.25	$152.20
Purchase #6	$41.41	13.645%	$47.0604	$47.06	$47.05	$47.10
Purchase #7	$48.50	12.132%	$54.384	$54.38	$54.40	$54.40
7 purchase totals =	$984.82		$1,086.0211	$1,086.02	$1,086.10	$1,086.00