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	$179.25	6.767%	$191.3798	$191.38	$191.40	$191.40
Purchase #2	$223.87	9.768%	$245.7376	$245.74	$245.75	$245.70
Purchase #3	$160.66	11.220%	$178.6861	$178.69	$178.70	$178.70
Purchase #4	$62.59	6.169%	$66.4512	$66.45	$66.45	$66.50
Purchase #5	$73.87	4.474%	$77.1749	$77.17	$77.15	$77.20
Purchase #6	$221.39	3.626%	$229.4176	$229.42	$229.40	$229.40
Purchase #7	$89.77	11.663%	$100.2399	$100.24	$100.25	$100.20
7 purchase totals =	$1,011.40		$1,089.0871	$1,089.09	$1,089.10	$1,089.10