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	$19.61	3.401%	$20.2769	$20.28	$20.30	$20.30
Purchase #2	$166.96	9.196%	$182.3136	$182.31	$182.30	$182.30
Purchase #3	$217.94	9.560%	$238.7751	$238.78	$238.80	$238.80
Purchase #4	$38.75	10.487%	$42.8137	$42.81	$42.80	$42.80
Purchase #5	$108.96	3.270%	$112.523	$112.52	$112.50	$112.50
Purchase #6	$175.59	11.179%	$195.2192	$195.22	$195.20	$195.20
Purchase #7	$17.77	9.668%	$19.488	$19.49	$19.50	$19.50
7 purchase totals =	$745.58		$811.4095	$811.41	$811.40	$811.40