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	$233.33	13.687%	$265.2659	$265.27	$265.25	$265.30
Purchase #2	$179.95	9.552%	$197.1388	$197.14	$197.15	$197.10
Purchase #3	$208.37	12.212%	$233.8161	$233.82	$233.80	$233.80
Purchase #4	$79.98	13.363%	$90.6677	$90.67	$90.65	$90.70
Purchase #5	$136.82	5.439%	$144.2616	$144.26	$144.25	$144.30
Purchase #6	$227.74	12.618%	$256.4762	$256.48	$256.50	$256.50
Purchase #7	$151.95	5.752%	$160.6902	$160.69	$160.70	$160.70
7 purchase totals =	$1,218.14		$1,348.3165	$1,348.33	$1,348.30	$1,348.40