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	$15.52	9.273%	$16.9592	$16.96	$16.95	$17.00
Purchase #2	$25.25	13.459%	$28.6484	$28.65	$28.65	$28.60
Purchase #3	$55.34	7.754%	$59.6311	$59.63	$59.65	$59.60
Purchase #4	$112.25	13.596%	$127.5115	$127.51	$127.50	$127.50
Purchase #5	$156.30	12.538%	$175.8969	$175.90	$175.90	$175.90
Purchase #6	$242.39	12.323%	$272.2597	$272.26	$272.25	$272.30
Purchase #7	$125.98	11.526%	$140.5005	$140.50	$140.50	$140.50
7 purchase totals =	$733.03		$821.4073	$821.41	$821.40	$821.40