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	$13.46	11.708%	$15.0359	$15.04	$15.05	$15.00
Purchase #2	$184.79	13.175%	$209.1361	$209.14	$209.15	$209.10
Purchase #3	$88.62	11.223%	$98.5658	$98.57	$98.55	$98.60
Purchase #4	$68.43	6.326%	$72.7589	$72.76	$72.75	$72.80
Purchase #5	$217.87	5.308%	$229.4345	$229.43	$229.45	$229.40
Purchase #6	$92.39	13.440%	$104.8072	$104.81	$104.80	$104.80
Purchase #7	$32.43	13.377%	$36.7682	$36.77	$36.75	$36.80
7 purchase totals =	$697.99		$766.5066	$766.52	$766.50	$766.50