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	$139.79	12.244%	$156.9059	$156.91	$156.90	$156.90
Purchase #2	$144.98	13.674%	$164.8046	$164.80	$164.80	$164.80
Purchase #3	$116.54	9.586%	$127.7115	$127.71	$127.70	$127.70
Purchase #4	$159.95	3.336%	$165.2859	$165.29	$165.30	$165.30
Purchase #5	$73.71	11.721%	$82.3495	$82.35	$82.35	$82.30
Purchase #6	$167.60	5.264%	$176.4225	$176.42	$176.40	$176.40
Purchase #7	$201.68	13.838%	$229.5885	$229.59	$229.60	$229.60
7 purchase totals =	$1,004.25		$1,103.0684	$1,103.07	$1,103.05	$1,103.00