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	$137.73	9.211%	$150.4163	$150.42	$150.40	$150.40
Purchase #2	$127.33	3.618%	$131.9368	$131.94	$131.95	$131.90
Purchase #3	$79.78	12.645%	$89.8682	$89.87	$89.85	$89.90
Purchase #4	$11.44	13.496%	$12.9839	$12.98	$13.00	$13.00
Purchase #5	$132.55	6.444%	$141.0915	$141.09	$141.10	$141.10
Purchase #6	$150.64	4.454%	$157.3495	$157.35	$157.35	$157.30
Purchase #7	$138.30	11.485%	$154.1838	$154.18	$154.20	$154.20
7 purchase totals =	$777.77		$837.8300	$837.83	$837.85	$837.80