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	$13.65	12.722%	$15.3866	$15.39	$15.40	$15.40
Purchase #2	$183.59	3.601%	$190.2011	$190.20	$190.20	$190.20
Purchase #3	$112.90	10.351%	$124.5863	$124.59	$124.60	$124.60
Purchase #4	$128.54	3.158%	$132.5993	$132.60	$132.60	$132.60
Purchase #5	$168.96	11.735%	$188.7875	$188.79	$188.80	$188.80
Purchase #6	$228.80	6.787%	$244.3287	$244.33	$244.35	$244.30
Purchase #7	$111.61	6.679%	$119.0644	$119.06	$119.05	$119.10
7 purchase totals =	$948.05		$1,014.9539	$1,014.96	$1,015.00	$1,015.00