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	$42.86	5.233%	$45.1029	$45.10	$45.10	$45.10
Purchase #2	$150.74	6.721%	$160.8712	$160.87	$160.85	$160.90
Purchase #3	$156.78	6.545%	$167.0413	$167.04	$167.05	$167.00
Purchase #4	$211.60	7.166%	$226.7633	$226.76	$226.75	$226.80
Purchase #5	$165.50	9.467%	$181.1679	$181.17	$181.15	$181.20
Purchase #6	$101.39	3.120%	$104.5534	$104.55	$104.55	$104.60
Purchase #7	$153.58	12.177%	$172.2814	$172.28	$172.30	$172.30
7 purchase totals =	$982.45		$1,057.7814	$1,057.77	$1,057.75	$1,057.90