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	$201.44	11.433%	$224.4706	$224.47	$224.45	$224.50
Purchase #2	$103.97	7.438%	$111.7033	$111.70	$111.70	$111.70
Purchase #3	$58.83	12.546%	$66.2108	$66.21	$66.20	$66.20
Purchase #4	$79.39	4.210%	$82.7323	$82.73	$82.75	$82.70
Purchase #5	$200.83	10.184%	$221.2825	$221.28	$221.30	$221.30
Purchase #6	$29.80	10.812%	$33.022	$33.02	$33.00	$33.00
Purchase #7	$216.59	12.804%	$244.3222	$244.32	$244.30	$244.30
7 purchase totals =	$890.85		$983.7437	$983.73	$983.70	$983.70