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	$31.76	8.358%	$34.4145	$34.41	$34.40	$34.40
Purchase #2	$85.25	4.453%	$89.0462	$89.05	$89.05	$89.00
Purchase #3	$80.88	11.368%	$90.0744	$90.07	$90.05	$90.10
Purchase #4	$19.70	5.550%	$20.7934	$20.79	$20.80	$20.80
Purchase #5	$76.46	13.454%	$86.7469	$86.75	$86.75	$86.70
Purchase #6	$42.71	12.522%	$48.0581	$48.06	$48.05	$48.10
Purchase #7	$146.60	13.478%	$166.3587	$166.36	$166.35	$166.40
7 purchase totals =	$483.36		$535.4922	$535.49	$535.45	$535.50