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	$35.40	12.286%	$39.7492	$39.75	$39.75	$39.70
Purchase #2	$112.32	13.667%	$127.6708	$127.67	$127.65	$127.70
Purchase #3	$234.69	10.194%	$258.6143	$258.61	$258.60	$258.60
Purchase #4	$189.36	7.357%	$203.2912	$203.29	$203.30	$203.30
Purchase #5	$219.45	11.581%	$244.8645	$244.86	$244.85	$244.90
Purchase #6	$196.57	4.587%	$205.5867	$205.59	$205.60	$205.60
Purchase #7	$77.66	5.768%	$82.1394	$82.14	$82.15	$82.10
7 purchase totals =	$1,065.45		$1,161.9161	$1,161.91	$1,161.90	$1,161.90