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	$7.32	5.429%	$7.7174	$7.72	$7.70	$7.70
Purchase #2	$134.43	4.562%	$140.5627	$140.56	$140.55	$140.60
Purchase #3	$27.39	13.627%	$31.1224	$31.12	$31.10	$31.10
Purchase #4	$218.59	6.855%	$233.5743	$233.57	$233.55	$233.60
Purchase #5	$112.52	10.154%	$123.9453	$123.95	$123.95	$123.90
Purchase #6	$214.60	4.717%	$224.7227	$224.72	$224.70	$224.70
Purchase #7	$50.94	4.312%	$53.1365	$53.14	$53.15	$53.10
7 purchase totals =	$765.79		$814.7813	$814.78	$814.70	$814.70