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	$227.82	11.106%	$253.1217	$253.12	$253.10	$253.10
Purchase #2	$30.50	5.168%	$32.0762	$32.08	$32.10	$32.10
Purchase #3	$183.34	7.159%	$196.4653	$196.47	$196.45	$196.50
Purchase #4	$138.73	13.363%	$157.2685	$157.27	$157.25	$157.30
Purchase #5	$249.90	5.195%	$262.8823	$262.88	$262.90	$262.90
Purchase #6	$209.79	6.142%	$222.6753	$222.68	$222.70	$222.70
Purchase #7	$82.69	6.750%	$88.2716	$88.27	$88.25	$88.30
7 purchase totals =	$1,122.77		$1,212.7609	$1,212.77	$1,212.75	$1,212.90