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	$35.89	7.430%	$38.5566	$38.56	$38.55	$38.60
Purchase #2	$42.97	4.164%	$44.7593	$44.76	$44.75	$44.80
Purchase #3	$42.85	4.514%	$44.7842	$44.78	$44.80	$44.80
Purchase #4	$227.53	12.873%	$256.8199	$256.82	$256.80	$256.80
Purchase #5	$186.49	5.420%	$196.5978	$196.60	$196.60	$196.60
Purchase #6	$107.83	3.865%	$111.9976	$112.00	$112.00	$112.00
Purchase #7	$229.85	3.372%	$237.6005	$237.60	$237.60	$237.60
7 purchase totals =	$873.41		$931.1159	$931.12	$931.10	$931.20