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	$241.96	10.680%	$267.8013	$267.80	$267.80	$267.80
Purchase #2	$233.47	12.870%	$263.5176	$263.52	$263.50	$263.50
Purchase #3	$128.52	10.568%	$142.102	$142.10	$142.10	$142.10
Purchase #4	$90.48	13.157%	$102.3845	$102.38	$102.40	$102.40
Purchase #5	$120.77	11.486%	$134.6416	$134.64	$134.65	$134.60
Purchase #6	$172.79	7.178%	$185.1929	$185.19	$185.20	$185.20
Purchase #7	$42.89	3.333%	$44.3195	$44.32	$44.30	$44.30
7 purchase totals =	$1,030.88		$1,139.9594	$1,139.95	$1,139.95	$1,139.90