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	$48.75	5.190%	$51.2801	$51.28	$51.30	$51.30
Purchase #2	$147.63	13.444%	$167.4774	$167.48	$167.50	$167.50
Purchase #3	$91.49	8.778%	$99.521	$99.52	$99.50	$99.50
Purchase #4	$107.56	3.280%	$111.088	$111.09	$111.10	$111.10
Purchase #5	$48.86	6.232%	$51.905	$51.91	$51.90	$51.90
Purchase #6	$113.75	9.263%	$124.2867	$124.29	$124.30	$124.30
Purchase #7	$24.87	11.815%	$27.8084	$27.81	$27.80	$27.80
7 purchase totals =	$582.91		$633.3666	$633.38	$633.40	$633.40