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	$25.86	10.249%	$28.5104	$28.51	$28.50	$28.50
Purchase #2	$8.49	12.370%	$9.5402	$9.54	$9.55	$9.50
Purchase #3	$230.43	6.710%	$245.8919	$245.89	$245.90	$245.90
Purchase #4	$29.58	12.636%	$33.3177	$33.32	$33.30	$33.30
Purchase #5	$237.93	10.206%	$262.2131	$262.21	$262.20	$262.20
Purchase #6	$56.52	9.144%	$61.6882	$61.69	$61.70	$61.70
Purchase #7	$199.45	11.383%	$222.1534	$222.15	$222.15	$222.20
7 purchase totals =	$788.26		$863.3149	$863.31	$863.30	$863.30