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	$81.34	8.194%	$88.005	$88.01	$88.00	$88.00
Purchase #2	$36.98	5.699%	$39.0875	$39.09	$39.10	$39.10
Purchase #3	$114.52	12.596%	$128.9449	$128.94	$128.95	$128.90
Purchase #4	$180.32	9.137%	$196.7958	$196.80	$196.80	$196.80
Purchase #5	$19.41	3.782%	$20.1441	$20.14	$20.15	$20.10
Purchase #6	$132.83	6.237%	$141.1146	$141.11	$141.10	$141.10
Purchase #7	$147.82	12.827%	$166.7809	$166.78	$166.80	$166.80
7 purchase totals =	$713.22		$780.8728	$780.87	$780.90	$780.80