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	$107.40	3.556%	$111.2191	$111.22	$111.20	$111.20
Purchase #2	$91.75	5.133%	$96.4595	$96.46	$96.45	$96.50
Purchase #3	$71.41	9.425%	$78.1404	$78.14	$78.15	$78.10
Purchase #4	$16.43	12.381%	$18.4642	$18.46	$18.45	$18.50
Purchase #5	$17.45	10.280%	$19.2439	$19.24	$19.25	$19.20
Purchase #6	$102.86	9.213%	$112.3365	$112.34	$112.35	$112.30
Purchase #7	$140.41	12.206%	$157.5484	$157.55	$157.55	$157.50
7 purchase totals =	$547.71		$593.4120	$593.41	$593.40	$593.30