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	$155.61	10.179%	$171.4495	$171.45	$171.45	$171.40
Purchase #2	$139.32	10.526%	$153.9848	$153.98	$154.00	$154.00
Purchase #3	$160.59	7.361%	$172.411	$172.41	$172.40	$172.40
Purchase #4	$43.35	7.239%	$46.4881	$46.49	$46.50	$46.50
Purchase #5	$175.42	9.304%	$191.7411	$191.74	$191.75	$191.70
Purchase #6	$81.38	9.192%	$88.8604	$88.86	$88.85	$88.90
Purchase #7	$62.27	7.489%	$66.9334	$66.93	$66.95	$66.90
7 purchase totals =	$817.94		$891.8683	$891.86	$891.90	$891.80