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	$228.59	4.364%	$238.5657	$238.57	$238.55	$238.60
Purchase #2	$32.93	13.735%	$37.4529	$37.45	$37.45	$37.50
Purchase #3	$151.79	8.555%	$164.7756	$164.78	$164.80	$164.80
Purchase #4	$243.77	7.839%	$262.8791	$262.88	$262.90	$262.90
Purchase #5	$31.71	9.545%	$34.7367	$34.74	$34.75	$34.70
Purchase #6	$94.65	8.343%	$102.5466	$102.55	$102.55	$102.50
Purchase #7	$119.97	12.456%	$134.9135	$134.91	$134.90	$134.90
7 purchase totals =	$903.41		$975.8701	$975.88	$975.90	$975.90