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	$38.57	9.233%	$42.1312	$42.13	$42.15	$42.10
Purchase #2	$222.35	7.521%	$239.0729	$239.07	$239.05	$239.10
Purchase #3	$230.54	13.277%	$261.1488	$261.15	$261.15	$261.10
Purchase #4	$208.99	7.121%	$223.8722	$223.87	$223.85	$223.90
Purchase #5	$130.44	8.624%	$141.6891	$141.69	$141.70	$141.70
Purchase #6	$75.51	4.441%	$78.8634	$78.86	$78.85	$78.90
Purchase #7	$113.84	11.571%	$127.0124	$127.01	$127.00	$127.00
7 purchase totals =	$1,020.24		$1,113.7900	$1,113.78	$1,113.75	$1,113.80