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	$41.71	3.426%	$43.139	$43.14	$43.15	$43.10
Purchase #2	$160.46	7.416%	$172.3597	$172.36	$172.35	$172.40
Purchase #3	$15.44	4.310%	$16.1055	$16.11	$16.10	$16.10
Purchase #4	$128.31	10.346%	$141.585	$141.59	$141.60	$141.60
Purchase #5	$11.41	6.444%	$12.1453	$12.15	$12.15	$12.10
Purchase #6	$63.69	10.164%	$70.1635	$70.16	$70.15	$70.20
Purchase #7	$167.71	11.372%	$186.782	$186.78	$186.80	$186.80
7 purchase totals =	$588.73		$642.2800	$642.29	$642.30	$642.30