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	$39.60	8.816%	$43.0911	$43.09	$43.10	$43.10
Purchase #2	$201.38	13.435%	$228.4354	$228.44	$228.45	$228.40
Purchase #3	$84.78	4.132%	$88.2831	$88.28	$88.30	$88.30
Purchase #4	$51.83	5.262%	$54.5573	$54.56	$54.55	$54.60
Purchase #5	$39.71	10.168%	$43.7477	$43.75	$43.75	$43.70
Purchase #6	$76.79	6.837%	$82.0401	$82.04	$82.05	$82.00
Purchase #7	$137.91	8.565%	$149.722	$149.72	$149.70	$149.70
7 purchase totals =	$632.00		$689.8767	$689.88	$689.90	$689.80