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	$157.72	13.730%	$179.375	$179.38	$179.40	$179.40
Purchase #2	$141.44	4.468%	$147.7595	$147.76	$147.75	$147.80
Purchase #3	$72.94	11.587%	$81.3916	$81.39	$81.40	$81.40
Purchase #4	$90.94	10.491%	$100.4805	$100.48	$100.50	$100.50
Purchase #5	$181.42	5.746%	$191.8444	$191.84	$191.85	$191.80
Purchase #6	$43.74	10.312%	$48.2505	$48.25	$48.25	$48.30
Purchase #7	$161.79	6.139%	$171.7223	$171.72	$171.70	$171.70
7 purchase totals =	$849.99		$920.8238	$920.82	$920.85	$920.90