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	$166.65	8.702%	$181.1519	$181.15	$181.15	$181.20
Purchase #2	$50.37	9.130%	$54.9688	$54.97	$54.95	$55.00
Purchase #3	$119.32	3.432%	$123.4151	$123.42	$123.40	$123.40
Purchase #4	$236.30	11.508%	$263.4934	$263.49	$263.50	$263.50
Purchase #5	$170.72	9.213%	$186.4484	$186.45	$186.45	$186.40
Purchase #6	$92.28	11.107%	$102.5295	$102.53	$102.55	$102.50
Purchase #7	$157.92	9.787%	$173.3756	$173.38	$173.40	$173.40
7 purchase totals =	$993.56		$1,085.3827	$1,085.39	$1,085.40	$1,085.40