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	$17.99	5.156%	$18.9176	$18.92	$18.90	$18.90
Purchase #2	$126.54	5.777%	$133.8502	$133.85	$133.85	$133.90
Purchase #3	$107.37	3.774%	$111.4221	$111.42	$111.40	$111.40
Purchase #4	$110.98	7.645%	$119.4644	$119.46	$119.45	$119.50
Purchase #5	$240.38	9.853%	$264.0646	$264.06	$264.05	$264.10
Purchase #6	$146.48	3.680%	$151.8705	$151.87	$151.85	$151.90
Purchase #7	$19.92	3.665%	$20.6501	$20.65	$20.65	$20.70
7 purchase totals =	$769.66		$820.2395	$820.23	$820.15	$820.40