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	$134.79	3.503%	$139.5117	$139.51	$139.50	$139.50
Purchase #2	$135.47	6.596%	$144.4056	$144.41	$144.40	$144.40
Purchase #3	$168.29	6.601%	$179.3988	$179.40	$179.40	$179.40
Purchase #4	$95.51	10.842%	$105.8652	$105.87	$105.85	$105.90
Purchase #5	$111.75	9.196%	$122.0265	$122.03	$122.05	$122.00
Purchase #6	$234.28	10.745%	$259.4534	$259.45	$259.45	$259.50
Purchase #7	$77.57	5.607%	$81.9193	$81.92	$81.90	$81.90
7 purchase totals =	$957.66		$1,032.5805	$1,032.59	$1,032.55	$1,032.60