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	$17.55	9.174%	$19.16	$19.16	$19.15	$19.20
Purchase #2	$233.37	10.370%	$257.5705	$257.57	$257.55	$257.60
Purchase #3	$17.86	3.496%	$18.4844	$18.48	$18.50	$18.50
Purchase #4	$92.50	13.863%	$105.3233	$105.32	$105.30	$105.30
Purchase #5	$117.91	4.358%	$123.0485	$123.05	$123.05	$123.00
Purchase #6	$186.51	5.274%	$196.3465	$196.35	$196.35	$196.30
Purchase #7	$142.62	3.273%	$147.288	$147.29	$147.30	$147.30
7 purchase totals =	$808.32		$867.2212	$867.22	$867.20	$867.20