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	$81.89	9.366%	$89.5598	$89.56	$89.55	$89.60
Purchase #2	$236.80	10.159%	$260.8565	$260.86	$260.85	$260.90
Purchase #3	$127.36	10.184%	$140.3303	$140.33	$140.35	$140.30
Purchase #4	$129.81	4.119%	$135.1569	$135.16	$135.15	$135.20
Purchase #5	$69.32	3.318%	$71.62	$71.62	$71.60	$71.60
Purchase #6	$62.96	7.528%	$67.6996	$67.70	$67.70	$67.70
Purchase #7	$48.69	12.288%	$54.673	$54.67	$54.65	$54.70
7 purchase totals =	$756.83		$819.8961	$819.90	$819.85	$820.00