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	$35.88	9.842%	$39.4113	$39.41	$39.40	$39.40
Purchase #2	$107.80	10.541%	$119.1632	$119.16	$119.15	$119.20
Purchase #3	$25.38	12.476%	$28.5464	$28.55	$28.55	$28.50
Purchase #4	$125.57	8.794%	$136.6126	$136.61	$136.60	$136.60
Purchase #5	$156.38	5.762%	$165.3906	$165.39	$165.40	$165.40
Purchase #6	$38.42	9.501%	$42.0703	$42.07	$42.05	$42.10
Purchase #7	$105.94	13.252%	$119.9792	$119.98	$120.00	$120.00
7 purchase totals =	$595.37		$651.1736	$651.17	$651.15	$651.20