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	$214.79	12.737%	$242.1478	$242.15	$242.15	$242.10
Purchase #2	$134.93	6.238%	$143.3469	$143.35	$143.35	$143.30
Purchase #3	$39.41	9.820%	$43.2801	$43.28	$43.30	$43.30
Purchase #4	$30.64	3.785%	$31.7997	$31.80	$31.80	$31.80
Purchase #5	$87.55	3.778%	$90.8576	$90.86	$90.85	$90.90
Purchase #6	$157.57	11.656%	$175.9364	$175.94	$175.95	$175.90
Purchase #7	$47.71	13.179%	$53.9977	$54.00	$54.00	$54.00
7 purchase totals =	$712.60		$781.3662	$781.38	$781.40	$781.30