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	$48.91	6.706%	$52.1899	$52.19	$52.20	$52.20
Purchase #2	$166.50	6.201%	$176.8247	$176.82	$176.80	$176.80
Purchase #3	$181.81	7.201%	$194.9021	$194.90	$194.90	$194.90
Purchase #4	$65.47	9.291%	$71.5528	$71.55	$71.55	$71.60
Purchase #5	$47.41	12.129%	$53.1604	$53.16	$53.15	$53.20
Purchase #6	$112.84	13.791%	$128.4018	$128.40	$128.40	$128.40
Purchase #7	$77.63	10.140%	$85.5017	$85.50	$85.50	$85.50
7 purchase totals =	$700.57		$762.5334	$762.52	$762.50	$762.60