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	$205.27	9.330%	$224.4217	$224.42	$224.40	$224.40
Purchase #2	$152.28	4.841%	$159.6519	$159.65	$159.65	$159.70
Purchase #3	$30.65	10.641%	$33.9115	$33.91	$33.90	$33.90
Purchase #4	$211.56	11.501%	$235.8915	$235.89	$235.90	$235.90
Purchase #5	$208.32	8.125%	$225.246	$225.25	$225.25	$225.20
Purchase #6	$43.54	7.614%	$46.8551	$46.86	$46.85	$46.90
Purchase #7	$77.75	10.350%	$85.7971	$85.80	$85.80	$85.80
7 purchase totals =	$929.37		$1,011.7748	$1,011.78	$1,011.75	$1,011.80