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	$122.89	4.280%	$128.1497	$128.15	$128.15	$128.10
Purchase #2	$201.71	7.355%	$216.5458	$216.55	$216.55	$216.50
Purchase #3	$51.89	3.655%	$53.7866	$53.79	$53.80	$53.80
Purchase #4	$19.53	10.206%	$21.5232	$21.52	$21.50	$21.50
Purchase #5	$59.46	5.568%	$62.7707	$62.77	$62.75	$62.80
Purchase #6	$54.93	10.381%	$60.6323	$60.63	$60.65	$60.60
Purchase #7	$124.89	7.477%	$134.228	$134.23	$134.25	$134.20
7 purchase totals =	$635.30		$677.6363	$677.64	$677.65	$677.50