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	$178.85	4.400%	$186.7194	$186.72	$186.70	$186.70
Purchase #2	$47.50	9.751%	$52.1317	$52.13	$52.15	$52.10
Purchase #3	$134.36	6.129%	$142.5949	$142.59	$142.60	$142.60
Purchase #4	$230.38	12.543%	$259.2766	$259.28	$259.30	$259.30
Purchase #5	$147.74	9.742%	$162.1328	$162.13	$162.15	$162.10
Purchase #6	$5.72	12.873%	$6.4563	$6.46	$6.45	$6.50
Purchase #7	$81.82	10.197%	$90.1632	$90.16	$90.15	$90.20
7 purchase totals =	$826.37		$899.4749	$899.47	$899.50	$899.50