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	$247.68	5.542%	$261.4064	$261.41	$261.40	$261.40
Purchase #2	$104.82	6.215%	$111.3346	$111.33	$111.35	$111.30
Purchase #3	$6.32	4.642%	$6.6134	$6.61	$6.60	$6.60
Purchase #4	$94.41	10.331%	$104.1635	$104.16	$104.15	$104.20
Purchase #5	$41.33	3.308%	$42.6972	$42.70	$42.70	$42.70
Purchase #6	$13.68	6.122%	$14.5175	$14.52	$14.50	$14.50
Purchase #7	$109.27	11.165%	$121.47	$121.47	$121.45	$121.50
7 purchase totals =	$617.51		$662.2026	$662.20	$662.15	$662.20