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	$90.42	10.237%	$99.6763	$99.68	$99.70	$99.70
Purchase #2	$45.26	9.294%	$49.4665	$49.47	$49.45	$49.50
Purchase #3	$129.45	9.740%	$142.0584	$142.06	$142.05	$142.10
Purchase #4	$49.51	13.552%	$56.2196	$56.22	$56.20	$56.20
Purchase #5	$53.36	12.871%	$60.228	$60.23	$60.25	$60.20
Purchase #6	$43.53	6.231%	$46.2424	$46.24	$46.25	$46.20
Purchase #7	$140.80	6.808%	$150.3857	$150.39	$150.40	$150.40
7 purchase totals =	$552.33		$604.2769	$604.29	$604.30	$604.30