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	$225.69	12.760%	$254.488	$254.49	$254.50	$254.50
Purchase #2	$67.53	8.145%	$73.0303	$73.03	$73.05	$73.00
Purchase #3	$116.71	12.210%	$130.9603	$130.96	$130.95	$131.00
Purchase #4	$189.87	12.328%	$213.2772	$213.28	$213.30	$213.30
Purchase #5	$80.75	3.571%	$83.6336	$83.63	$83.65	$83.60
Purchase #6	$35.89	3.724%	$37.2265	$37.23	$37.25	$37.20
Purchase #7	$122.41	4.237%	$127.5965	$127.60	$127.60	$127.60
7 purchase totals =	$838.85		$920.2124	$920.22	$920.30	$920.20