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	$71.68	9.198%	$78.2731	$78.27	$78.25	$78.30
Purchase #2	$244.32	8.572%	$265.2631	$265.26	$265.25	$265.30
Purchase #3	$28.72	10.307%	$31.6802	$31.68	$31.70	$31.70
Purchase #4	$62.28	6.835%	$66.5368	$66.54	$66.55	$66.50
Purchase #5	$237.37	10.757%	$262.9039	$262.90	$262.90	$262.90
Purchase #6	$87.36	6.121%	$92.7073	$92.71	$92.70	$92.70
Purchase #7	$122.61	11.368%	$136.5483	$136.55	$136.55	$136.50
7 purchase totals =	$854.34		$933.9127	$933.91	$933.90	$933.90