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	$88.29	13.643%	$100.3354	$100.34	$100.35	$100.30
Purchase #2	$89.83	7.128%	$96.2331	$96.23	$96.25	$96.20
Purchase #3	$232.61	5.584%	$245.5989	$245.60	$245.60	$245.60
Purchase #4	$128.92	12.856%	$145.494	$145.49	$145.50	$145.50
Purchase #5	$5.36	8.428%	$5.8117	$5.81	$5.80	$5.80
Purchase #6	$77.88	13.573%	$88.4507	$88.45	$88.45	$88.50
Purchase #7	$127.69	8.213%	$138.1772	$138.18	$138.20	$138.20
7 purchase totals =	$750.58		$820.1010	$820.10	$820.15	$820.10