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	$18.59	4.443%	$19.416	$19.42	$19.40	$19.40
Purchase #2	$68.55	5.602%	$72.3902	$72.39	$72.40	$72.40
Purchase #3	$245.29	9.361%	$268.2516	$268.25	$268.25	$268.30
Purchase #4	$32.45	13.610%	$36.8664	$36.87	$36.85	$36.90
Purchase #5	$17.61	4.485%	$18.3998	$18.40	$18.40	$18.40
Purchase #6	$137.77	3.551%	$142.6622	$142.66	$142.65	$142.70
Purchase #7	$78.42	12.631%	$88.3252	$88.33	$88.35	$88.30
7 purchase totals =	$598.68		$646.3114	$646.32	$646.30	$646.40