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	$70.45	11.763%	$78.737	$78.74	$78.75	$78.70
Purchase #2	$34.30	9.819%	$37.6679	$37.67	$37.65	$37.70
Purchase #3	$237.62	8.524%	$257.8747	$257.87	$257.85	$257.90
Purchase #4	$164.39	4.544%	$171.8599	$171.86	$171.85	$171.90
Purchase #5	$49.92	10.752%	$55.2874	$55.29	$55.30	$55.30
Purchase #6	$94.93	13.572%	$107.8139	$107.81	$107.80	$107.80
Purchase #7	$73.62	11.800%	$82.3072	$82.31	$82.30	$82.30
7 purchase totals =	$725.23		$791.5480	$791.55	$791.50	$791.60