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	$102.71	3.712%	$106.5226	$106.52	$106.50	$106.50
Purchase #2	$240.59	7.785%	$259.3199	$259.32	$259.30	$259.30
Purchase #3	$49.67	8.812%	$54.0469	$54.05	$54.05	$54.00
Purchase #4	$110.33	7.739%	$118.8684	$118.87	$118.85	$118.90
Purchase #5	$222.40	5.451%	$234.523	$234.52	$234.50	$234.50
Purchase #6	$19.31	11.556%	$21.5415	$21.54	$21.55	$21.50
Purchase #7	$99.35	4.241%	$103.5634	$103.56	$103.55	$103.60
7 purchase totals =	$844.36		$898.3857	$898.38	$898.30	$898.30