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	$79.75	11.629%	$89.0241	$89.02	$89.00	$89.00
Purchase #2	$164.31	9.336%	$179.65	$179.65	$179.65	$179.70
Purchase #3	$67.97	10.481%	$75.0939	$75.09	$75.10	$75.10
Purchase #4	$140.27	13.353%	$159.0003	$159.00	$159.00	$159.00
Purchase #5	$164.44	8.769%	$178.8597	$178.86	$178.85	$178.90
Purchase #6	$175.35	12.240%	$196.8128	$196.81	$196.80	$196.80
Purchase #7	$9.73	11.157%	$10.8156	$10.82	$10.80	$10.80
7 purchase totals =	$801.82		$889.2564	$889.25	$889.20	$889.30