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	$135.34	6.866%	$144.6324	$144.63	$144.65	$144.60
Purchase #2	$61.33	6.191%	$65.1269	$65.13	$65.15	$65.10
Purchase #3	$198.41	6.110%	$210.5329	$210.53	$210.55	$210.50
Purchase #4	$118.93	3.593%	$123.2032	$123.20	$123.20	$123.20
Purchase #5	$89.96	13.810%	$102.3835	$102.38	$102.40	$102.40
Purchase #6	$237.35	5.545%	$250.5111	$250.51	$250.50	$250.50
Purchase #7	$167.62	3.446%	$173.3962	$173.40	$173.40	$173.40
7 purchase totals =	$1,008.94		$1,069.7862	$1,069.78	$1,069.85	$1,069.70