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	$200.37	13.451%	$227.3218	$227.32	$227.30	$227.30
Purchase #2	$121.33	5.406%	$127.8891	$127.89	$127.90	$127.90
Purchase #3	$218.95	4.751%	$229.3523	$229.35	$229.35	$229.40
Purchase #4	$213.50	10.324%	$235.5417	$235.54	$235.55	$235.50
Purchase #5	$162.75	9.553%	$178.2975	$178.30	$178.30	$178.30
Purchase #6	$194.42	7.203%	$208.4241	$208.42	$208.40	$208.40
Purchase #7	$121.56	8.290%	$131.6373	$131.64	$131.65	$131.60
7 purchase totals =	$1,232.88		$1,338.4638	$1,338.46	$1,338.45	$1,338.40