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	$35.57	9.383%	$38.9075	$38.91	$38.90	$38.90
Purchase #2	$229.78	8.770%	$249.9317	$249.93	$249.95	$249.90
Purchase #3	$13.38	6.371%	$14.2324	$14.23	$14.25	$14.20
Purchase #4	$212.73	11.682%	$237.5811	$237.58	$237.60	$237.60
Purchase #5	$187.83	4.758%	$196.767	$196.77	$196.75	$196.80
Purchase #6	$119.70	6.384%	$127.3416	$127.34	$127.35	$127.30
Purchase #7	$26.48	3.563%	$27.4235	$27.42	$27.40	$27.40
7 purchase totals =	$825.47		$892.1848	$892.18	$892.20	$892.10