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	$200.46	11.112%	$222.7351	$222.74	$222.75	$222.70
Purchase #2	$209.58	13.868%	$238.6446	$238.64	$238.65	$238.60
Purchase #3	$10.41	11.832%	$11.6417	$11.64	$11.65	$11.60
Purchase #4	$93.33	10.696%	$103.3126	$103.31	$103.30	$103.30
Purchase #5	$15.47	12.423%	$17.3918	$17.39	$17.40	$17.40
Purchase #6	$18.60	7.125%	$19.9253	$19.93	$19.95	$19.90
Purchase #7	$36.42	3.814%	$37.8091	$37.81	$37.80	$37.80
7 purchase totals =	$584.27		$651.4602	$651.46	$651.50	$651.30