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	$24.51	11.476%	$27.3228	$27.32	$27.30	$27.30
Purchase #2	$37.66	5.872%	$39.8714	$39.87	$39.85	$39.90
Purchase #3	$181.25	4.762%	$189.8811	$189.88	$189.90	$189.90
Purchase #4	$176.72	6.164%	$187.613	$187.61	$187.60	$187.60
Purchase #5	$27.82	13.801%	$31.6594	$31.66	$31.65	$31.70
Purchase #6	$18.29	8.657%	$19.8734	$19.87	$19.85	$19.90
Purchase #7	$43.27	4.580%	$45.2518	$45.25	$45.25	$45.30
7 purchase totals =	$509.52		$541.4729	$541.46	$541.40	$541.60