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	$26.89	10.220%	$29.6382	$29.64	$29.65	$29.60
Purchase #2	$20.75	7.747%	$22.3575	$22.36	$22.35	$22.40
Purchase #3	$135.30	6.712%	$144.3813	$144.38	$144.40	$144.40
Purchase #4	$220.93	7.673%	$237.882	$237.88	$237.90	$237.90
Purchase #5	$127.29	3.348%	$131.5517	$131.55	$131.55	$131.60
Purchase #6	$188.78	10.592%	$208.7756	$208.78	$208.80	$208.80
Purchase #7	$53.39	11.288%	$59.4167	$59.42	$59.40	$59.40
7 purchase totals =	$773.33		$834.0030	$834.01	$834.05	$834.10