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	$173.54	11.738%	$193.9101	$193.91	$193.90	$193.90
Purchase #2	$58.60	13.103%	$66.2784	$66.28	$66.30	$66.30
Purchase #3	$73.41	8.873%	$79.9237	$79.92	$79.90	$79.90
Purchase #4	$71.30	6.503%	$75.9366	$75.94	$75.95	$75.90
Purchase #5	$69.75	12.499%	$78.4681	$78.47	$78.45	$78.50
Purchase #6	$229.33	12.454%	$257.8908	$257.89	$257.90	$257.90
Purchase #7	$188.42	4.513%	$196.9234	$196.92	$196.90	$196.90
7 purchase totals =	$864.35		$949.3311	$949.33	$949.30	$949.30