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	$17.27	12.767%	$19.4749	$19.47	$19.45	$19.50
Purchase #2	$18.59	10.568%	$20.5546	$20.55	$20.55	$20.60
Purchase #3	$191.55	7.390%	$205.7055	$205.71	$205.70	$205.70
Purchase #4	$207.85	5.717%	$219.7328	$219.73	$219.75	$219.70
Purchase #5	$88.94	7.293%	$95.4264	$95.43	$95.45	$95.40
Purchase #6	$237.73	5.371%	$250.4985	$250.50	$250.50	$250.50
Purchase #7	$79.29	12.449%	$89.1608	$89.16	$89.15	$89.20
7 purchase totals =	$841.22		$900.5535	$900.55	$900.55	$900.60