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	$90.78	9.565%	$99.4631	$99.46	$99.45	$99.50
Purchase #2	$156.65	7.856%	$168.9564	$168.96	$168.95	$169.00
Purchase #3	$94.62	11.548%	$105.5467	$105.55	$105.55	$105.50
Purchase #4	$149.49	4.385%	$156.0451	$156.05	$156.05	$156.00
Purchase #5	$177.69	3.674%	$184.2183	$184.22	$184.20	$184.20
Purchase #6	$73.41	13.182%	$83.0869	$83.09	$83.10	$83.10
Purchase #7	$177.47	3.384%	$183.4756	$183.48	$183.50	$183.50
7 purchase totals =	$920.11		$980.7921	$980.81	$980.80	$980.80