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	$108.56	13.694%	$123.4262	$123.43	$123.45	$123.40
Purchase #2	$174.53	3.259%	$180.2179	$180.22	$180.20	$180.20
Purchase #3	$107.74	11.119%	$119.7196	$119.72	$119.70	$119.70
Purchase #4	$213.30	9.569%	$233.7107	$233.71	$233.70	$233.70
Purchase #5	$43.98	5.669%	$46.4732	$46.47	$46.45	$46.50
Purchase #6	$80.61	7.384%	$86.5622	$86.56	$86.55	$86.60
Purchase #7	$237.44	12.171%	$266.3388	$266.34	$266.35	$266.30
7 purchase totals =	$966.16		$1,056.4486	$1,056.45	$1,056.40	$1,056.40