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	$25.39	8.401%	$27.523	$27.52	$27.50	$27.50
Purchase #2	$88.76	9.208%	$96.933	$96.93	$96.95	$96.90
Purchase #3	$158.91	3.392%	$164.3002	$164.30	$164.30	$164.30
Purchase #4	$117.46	8.285%	$127.1916	$127.19	$127.20	$127.20
Purchase #5	$235.30	8.605%	$255.5476	$255.55	$255.55	$255.50
Purchase #6	$131.33	3.837%	$136.3691	$136.37	$136.35	$136.40
Purchase #7	$143.28	10.711%	$158.6267	$158.63	$158.65	$158.60
7 purchase totals =	$900.43		$966.4912	$966.49	$966.50	$966.40