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	$42.80	6.206%	$45.4562	$45.46	$45.45	$45.50
Purchase #2	$164.69	13.206%	$186.439	$186.44	$186.45	$186.40
Purchase #3	$76.75	8.562%	$83.3213	$83.32	$83.30	$83.30
Purchase #4	$31.90	11.837%	$35.676	$35.68	$35.70	$35.70
Purchase #5	$11.46	4.743%	$12.0035	$12.00	$12.00	$12.00
Purchase #6	$182.35	12.561%	$205.255	$205.26	$205.25	$205.30
Purchase #7	$78.45	9.547%	$85.9396	$85.94	$85.95	$85.90
7 purchase totals =	$588.40		$654.0906	$654.10	$654.10	$654.10