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	$103.60	3.402%	$107.1245	$107.12	$107.10	$107.10
Purchase #2	$41.29	11.870%	$46.1911	$46.19	$46.20	$46.20
Purchase #3	$140.42	7.260%	$150.6145	$150.61	$150.60	$150.60
Purchase #4	$25.55	11.573%	$28.5069	$28.51	$28.50	$28.50
Purchase #5	$52.81	11.314%	$58.7849	$58.78	$58.80	$58.80
Purchase #6	$141.31	4.240%	$147.3015	$147.30	$147.30	$147.30
Purchase #7	$100.63	5.189%	$105.8517	$105.85	$105.85	$105.90
7 purchase totals =	$605.61		$644.3751	$644.36	$644.35	$644.40