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	$122.36	13.626%	$139.0328	$139.03	$139.05	$139.00
Purchase #2	$239.98	7.330%	$257.5705	$257.57	$257.55	$257.60
Purchase #3	$149.60	11.369%	$166.608	$166.61	$166.60	$166.60
Purchase #4	$124.29	13.873%	$141.5328	$141.53	$141.55	$141.50
Purchase #5	$131.73	11.152%	$146.4205	$146.42	$146.40	$146.40
Purchase #6	$132.72	9.648%	$145.5248	$145.52	$145.50	$145.50
Purchase #7	$129.31	12.518%	$145.497	$145.50	$145.50	$145.50
7 purchase totals =	$1,029.99		$1,142.1864	$1,142.18	$1,142.15	$1,142.10