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	$71.45	10.109%	$78.6729	$78.67	$78.65	$78.70
Purchase #2	$220.34	3.746%	$228.5939	$228.59	$228.60	$228.60
Purchase #3	$35.97	7.608%	$38.7066	$38.71	$38.70	$38.70
Purchase #4	$144.54	5.364%	$152.2931	$152.29	$152.30	$152.30
Purchase #5	$232.89	10.637%	$257.6625	$257.66	$257.65	$257.70
Purchase #6	$243.87	5.196%	$256.5415	$256.54	$256.55	$256.50
Purchase #7	$134.25	6.226%	$142.6084	$142.61	$142.60	$142.60
7 purchase totals =	$1,083.31		$1,155.0789	$1,155.07	$1,155.05	$1,155.10