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	$27.37	8.294%	$29.6401	$29.64	$29.65	$29.60
Purchase #2	$97.59	12.193%	$109.4891	$109.49	$109.50	$109.50
Purchase #3	$100.64	3.133%	$103.7931	$103.79	$103.80	$103.80
Purchase #4	$227.42	7.498%	$244.472	$244.47	$244.45	$244.50
Purchase #5	$12.94	7.385%	$13.8956	$13.90	$13.90	$13.90
Purchase #6	$44.43	5.411%	$46.8341	$46.83	$46.85	$46.80
Purchase #7	$35.62	11.371%	$39.6704	$39.67	$39.65	$39.70
7 purchase totals =	$546.01		$587.7944	$587.79	$587.80	$587.80