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	$148.54	13.475%	$168.5558	$168.56	$168.55	$168.60
Purchase #2	$143.40	8.650%	$155.8041	$155.80	$155.80	$155.80
Purchase #3	$90.71	12.226%	$101.8002	$101.80	$101.80	$101.80
Purchase #4	$146.84	8.200%	$158.8809	$158.88	$158.90	$158.90
Purchase #5	$65.30	11.507%	$72.8141	$72.81	$72.80	$72.80
Purchase #6	$105.45	4.745%	$110.4536	$110.45	$110.45	$110.50
Purchase #7	$102.27	9.232%	$111.7116	$111.71	$111.70	$111.70
7 purchase totals =	$802.51		$880.0203	$880.01	$880.00	$880.10