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	$213.30	5.663%	$225.3792	$225.38	$225.40	$225.40
Purchase #2	$248.96	12.440%	$279.9306	$279.93	$279.95	$279.90
Purchase #3	$161.38	12.353%	$181.3153	$181.32	$181.30	$181.30
Purchase #4	$175.64	5.209%	$184.7891	$184.79	$184.80	$184.80
Purchase #5	$101.93	11.181%	$113.3268	$113.33	$113.35	$113.30
Purchase #6	$119.37	6.874%	$127.5755	$127.58	$127.60	$127.60
Purchase #7	$127.73	7.838%	$137.7415	$137.74	$137.75	$137.70
7 purchase totals =	$1,148.31		$1,250.0580	$1,250.07	$1,250.15	$1,250.00