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	$225.64	3.380%	$233.2666	$233.27	$233.25	$233.30
Purchase #2	$55.82	5.735%	$59.0213	$59.02	$59.00	$59.00
Purchase #3	$149.84	11.474%	$167.0326	$167.03	$167.05	$167.00
Purchase #4	$21.94	13.690%	$24.9436	$24.94	$24.95	$24.90
Purchase #5	$205.87	13.393%	$233.4422	$233.44	$233.45	$233.40
Purchase #6	$143.39	11.609%	$160.0361	$160.04	$160.05	$160.00
Purchase #7	$29.83	5.565%	$31.49	$31.49	$31.50	$31.50
7 purchase totals =	$832.33		$909.2324	$909.23	$909.25	$909.10