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	$128.26	6.495%	$136.5905	$136.59	$136.60	$136.60
Purchase #2	$234.97	12.253%	$263.7609	$263.76	$263.75	$263.80
Purchase #3	$140.55	7.490%	$151.0772	$151.08	$151.10	$151.10
Purchase #4	$54.77	3.737%	$56.8168	$56.82	$56.80	$56.80
Purchase #5	$168.86	12.697%	$190.3002	$190.30	$190.30	$190.30
Purchase #6	$142.56	13.646%	$162.0137	$162.01	$162.00	$162.00
Purchase #7	$38.94	11.424%	$43.3885	$43.39	$43.40	$43.40
7 purchase totals =	$908.91		$1,003.9478	$1,003.95	$1,003.95	$1,004.00