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	$160.59	11.716%	$179.4047	$179.40	$179.40	$179.40
Purchase #2	$117.56	8.517%	$127.5726	$127.57	$127.55	$127.60
Purchase #3	$195.88	10.162%	$215.7853	$215.79	$215.80	$215.80
Purchase #4	$127.80	4.400%	$133.4232	$133.42	$133.40	$133.40
Purchase #5	$10.88	4.592%	$11.3796	$11.38	$11.40	$11.40
Purchase #6	$139.44	5.763%	$147.4759	$147.48	$147.50	$147.50
Purchase #7	$47.69	11.673%	$53.2569	$53.26	$53.25	$53.30
7 purchase totals =	$799.84		$868.2982	$868.30	$868.30	$868.40