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	$27.45	9.151%	$29.9619	$29.96	$29.95	$30.00
Purchase #2	$103.72	7.871%	$111.8838	$111.88	$111.90	$111.90
Purchase #3	$150.60	6.449%	$160.3122	$160.31	$160.30	$160.30
Purchase #4	$147.41	4.121%	$153.4848	$153.48	$153.50	$153.50
Purchase #5	$89.87	3.572%	$93.0802	$93.08	$93.10	$93.10
Purchase #6	$65.53	11.459%	$73.0391	$73.04	$73.05	$73.00
Purchase #7	$38.36	7.124%	$41.0928	$41.09	$41.10	$41.10
7 purchase totals =	$622.94		$662.8548	$662.84	$662.90	$662.90