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	$107.89	3.614%	$111.7891	$111.79	$111.80	$111.80
Purchase #2	$39.55	6.436%	$42.0954	$42.10	$42.10	$42.10
Purchase #3	$41.35	4.461%	$43.1946	$43.19	$43.20	$43.20
Purchase #4	$24.52	13.443%	$27.8162	$27.82	$27.80	$27.80
Purchase #5	$147.82	8.622%	$160.565	$160.57	$160.55	$160.60
Purchase #6	$204.96	3.103%	$211.3199	$211.32	$211.30	$211.30
Purchase #7	$63.89	10.266%	$70.4489	$70.45	$70.45	$70.40
7 purchase totals =	$629.98		$667.2291	$667.24	$667.20	$667.20