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	$41.70	8.117%	$45.0848	$45.08	$45.10	$45.10
Purchase #2	$244.82	4.715%	$256.3633	$256.36	$256.35	$256.40
Purchase #3	$167.90	8.314%	$181.8592	$181.86	$181.85	$181.90
Purchase #4	$20.93	4.470%	$21.8656	$21.87	$21.85	$21.90
Purchase #5	$15.91	3.310%	$16.4366	$16.44	$16.45	$16.40
Purchase #6	$102.25	8.619%	$111.0629	$111.06	$111.05	$111.10
Purchase #7	$131.72	12.238%	$147.8399	$147.84	$147.85	$147.80
7 purchase totals =	$725.23		$780.5123	$780.51	$780.50	$780.60