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	$13.32	12.675%	$15.0083	$15.01	$15.00	$15.00
Purchase #2	$99.47	10.384%	$109.799	$109.80	$109.80	$109.80
Purchase #3	$212.89	9.126%	$232.3183	$232.32	$232.30	$232.30
Purchase #4	$89.95	10.174%	$99.1015	$99.10	$99.10	$99.10
Purchase #5	$230.42	7.430%	$247.5402	$247.54	$247.55	$247.50
Purchase #6	$250.87	10.189%	$276.4311	$276.43	$276.45	$276.40
Purchase #7	$17.56	10.502%	$19.4042	$19.40	$19.40	$19.40
7 purchase totals =	$914.48		$999.6026	$999.60	$999.60	$999.50