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	$137.92	4.394%	$143.9802	$143.98	$144.00	$144.00
Purchase #2	$79.81	13.491%	$90.5772	$90.58	$90.60	$90.60
Purchase #3	$127.28	10.368%	$140.4764	$140.48	$140.50	$140.50
Purchase #4	$197.68	7.531%	$212.5673	$212.57	$212.55	$212.60
Purchase #5	$171.59	8.647%	$186.4274	$186.43	$186.45	$186.40
Purchase #6	$145.57	3.267%	$150.3258	$150.33	$150.35	$150.30
Purchase #7	$90.28	3.685%	$93.6068	$93.61	$93.60	$93.60
7 purchase totals =	$950.13		$1,017.9611	$1,017.98	$1,018.05	$1,018.00