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	$17.79	12.265%	$19.9719	$19.97	$19.95	$20.00
Purchase #2	$72.50	9.732%	$79.5557	$79.56	$79.55	$79.60
Purchase #3	$153.80	10.440%	$169.8567	$169.86	$169.85	$169.90
Purchase #4	$133.73	6.647%	$142.619	$142.62	$142.60	$142.60
Purchase #5	$201.51	9.218%	$220.0852	$220.09	$220.10	$220.10
Purchase #6	$54.70	12.545%	$61.5621	$61.56	$61.55	$61.60
Purchase #7	$188.36	4.259%	$196.3823	$196.38	$196.40	$196.40
7 purchase totals =	$822.39		$890.0329	$890.04	$890.00	$890.20