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	$243.82	6.853%	$260.529	$260.53	$260.55	$260.50
Purchase #2	$170.61	5.135%	$179.3708	$179.37	$179.35	$179.40
Purchase #3	$250.90	7.726%	$270.2845	$270.28	$270.30	$270.30
Purchase #4	$245.46	10.708%	$271.7439	$271.74	$271.75	$271.70
Purchase #5	$167.76	13.445%	$190.3153	$190.32	$190.30	$190.30
Purchase #6	$52.83	12.575%	$59.4734	$59.47	$59.45	$59.50
Purchase #7	$16.76	5.508%	$17.6831	$17.68	$17.70	$17.70
7 purchase totals =	$1,148.14		$1,249.4000	$1,249.39	$1,249.40	$1,249.40