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	$40.28	8.705%	$43.7864	$43.79	$43.80	$43.80
Purchase #2	$67.87	9.254%	$74.1507	$74.15	$74.15	$74.20
Purchase #3	$131.41	5.820%	$139.0581	$139.06	$139.05	$139.10
Purchase #4	$91.31	13.584%	$103.7136	$103.71	$103.70	$103.70
Purchase #5	$201.88	9.575%	$221.21	$221.21	$221.20	$221.20
Purchase #6	$94.37	10.504%	$104.2826	$104.28	$104.30	$104.30
Purchase #7	$38.41	5.781%	$40.6305	$40.63	$40.65	$40.60
7 purchase totals =	$665.53		$726.8319	$726.83	$726.85	$726.90