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	$27.42	9.561%	$30.0416	$30.04	$30.05	$30.00
Purchase #2	$76.82	8.126%	$83.0624	$83.06	$83.05	$83.10
Purchase #3	$90.44	11.431%	$100.7782	$100.78	$100.80	$100.80
Purchase #4	$74.81	9.220%	$81.7075	$81.71	$81.70	$81.70
Purchase #5	$38.38	10.592%	$42.4452	$42.45	$42.45	$42.40
Purchase #6	$246.27	7.581%	$264.9397	$264.94	$264.95	$264.90
Purchase #7	$82.62	3.798%	$85.7579	$85.76	$85.75	$85.80
7 purchase totals =	$636.76		$688.7325	$688.74	$688.75	$688.70