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	$89.86	11.802%	$100.4653	$100.47	$100.45	$100.50
Purchase #2	$160.58	7.349%	$172.381	$172.38	$172.40	$172.40
Purchase #3	$17.37	11.296%	$19.3321	$19.33	$19.35	$19.30
Purchase #4	$47.56	12.621%	$53.5625	$53.56	$53.55	$53.60
Purchase #5	$189.44	10.639%	$209.5945	$209.59	$209.60	$209.60
Purchase #6	$122.38	6.680%	$130.555	$130.56	$130.55	$130.60
Purchase #7	$120.45	11.554%	$134.3668	$134.37	$134.35	$134.40
7 purchase totals =	$747.64		$820.2572	$820.26	$820.25	$820.40