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	$112.82	4.223%	$117.5844	$117.58	$117.60	$117.60
Purchase #2	$33.49	7.609%	$36.0383	$36.04	$36.05	$36.00
Purchase #3	$71.70	8.173%	$77.56	$77.56	$77.55	$77.60
Purchase #4	$16.73	13.125%	$18.9258	$18.93	$18.95	$18.90
Purchase #5	$206.70	10.190%	$227.7627	$227.76	$227.75	$227.80
Purchase #6	$82.53	9.543%	$90.4058	$90.41	$90.40	$90.40
Purchase #7	$92.88	8.177%	$100.4748	$100.47	$100.45	$100.50
7 purchase totals =	$616.85		$668.7518	$668.75	$668.75	$668.80