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	$7.97	6.265%	$8.4693	$8.47	$8.45	$8.50
Purchase #2	$159.90	5.363%	$168.4754	$168.48	$168.50	$168.50
Purchase #3	$105.45	5.514%	$111.2645	$111.26	$111.25	$111.30
Purchase #4	$164.68	12.329%	$184.9834	$184.98	$185.00	$185.00
Purchase #5	$158.46	8.403%	$171.7754	$171.78	$171.80	$171.80
Purchase #6	$53.56	11.565%	$59.7542	$59.75	$59.75	$59.80
Purchase #7	$188.41	8.281%	$204.0122	$204.01	$204.00	$204.00
7 purchase totals =	$838.43		$908.7344	$908.73	$908.75	$908.90