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	$137.54	10.353%	$151.7795	$151.78	$151.80	$151.80
Purchase #2	$124.93	9.414%	$136.6909	$136.69	$136.70	$136.70
Purchase #3	$19.32	8.598%	$20.9811	$20.98	$21.00	$21.00
Purchase #4	$121.39	5.704%	$128.3141	$128.31	$128.30	$128.30
Purchase #5	$103.44	8.728%	$112.4682	$112.47	$112.45	$112.50
Purchase #6	$171.38	11.731%	$191.4846	$191.48	$191.50	$191.50
Purchase #7	$80.72	5.185%	$84.9053	$84.91	$84.90	$84.90
7 purchase totals =	$758.72		$826.6237	$826.62	$826.65	$826.70