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	$243.54	6.480%	$259.3214	$259.32	$259.30	$259.30
Purchase #2	$168.60	8.430%	$182.813	$182.81	$182.80	$182.80
Purchase #3	$22.50	3.744%	$23.3424	$23.34	$23.35	$23.30
Purchase #4	$175.25	5.632%	$185.1201	$185.12	$185.10	$185.10
Purchase #5	$97.96	13.699%	$111.3795	$111.38	$111.40	$111.40
Purchase #6	$116.78	11.599%	$130.3253	$130.33	$130.35	$130.30
Purchase #7	$63.75	5.455%	$67.2276	$67.23	$67.25	$67.20
7 purchase totals =	$888.38		$959.5293	$959.53	$959.55	$959.40