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	$26.42	13.751%	$30.053	$30.05	$30.05	$30.10
Purchase #2	$19.44	4.645%	$20.343	$20.34	$20.35	$20.30
Purchase #3	$26.44	13.452%	$29.9967	$30.00	$30.00	$30.00
Purchase #4	$152.66	5.267%	$160.7006	$160.70	$160.70	$160.70
Purchase #5	$97.86	5.740%	$103.4772	$103.48	$103.50	$103.50
Purchase #6	$92.59	12.150%	$103.8397	$103.84	$103.85	$103.80
Purchase #7	$72.76	7.852%	$78.4731	$78.47	$78.45	$78.50
7 purchase totals =	$488.17		$526.8833	$526.88	$526.90	$526.90