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	$121.93	5.746%	$128.9361	$128.94	$128.95	$128.90
Purchase #2	$174.34	3.223%	$179.959	$179.96	$179.95	$180.00
Purchase #3	$96.64	9.238%	$105.5676	$105.57	$105.55	$105.60
Purchase #4	$48.59	9.520%	$53.2158	$53.22	$53.20	$53.20
Purchase #5	$174.81	13.757%	$198.8586	$198.86	$198.85	$198.90
Purchase #6	$9.59	11.718%	$10.7138	$10.71	$10.70	$10.70
Purchase #7	$95.95	11.320%	$106.8115	$106.81	$106.80	$106.80
7 purchase totals =	$721.85		$784.0624	$784.07	$784.00	$784.10